Force Unit: Pre-Test Name _________________________________

____1) The moon remains in its orbit around the Earth because of the interaction (attractive force) between the Earth and moon. Which of the following statements is true?

A) The moon does not interact with the other planets in our solar system.B) The moon does not interact with the sun.C) The interactions that the moon has with other planets and the sun are smaller because of the

larger distance between the moon and these other objects.D) There is no interaction between the Earth and the moon.

____2) Situation 1: A tow truck attaches a car to the truck using a chain. Situation 2: Two magnets are brought near one another with one north pole approaching the other magnet's south pole; the magnets attract each other, but they are not allowed to make contact. Which situation describes a contact force?

A) Only the magnets attracting each other since contact is prevented.B) Only the tow truck-car system describes a contact force because the chain touches both the

tow truck and the car.C) Both of the systems describe a contact force since one object is interacting with another object.D) Neither system describes a contact force because the force between the magnets moves the magnets without contact and the chain is used to connect the car and the tow truck.

____3) A car is stopped at a red light. When the light turns green, the car accelerates forward. As the car accelerates, A) there must be a net force acting on the car. B) there is only a net force if the driver presses the accelerator all the way to the floor. C) there is no net force since the car is approaching a constant velocity. D) there is not enough information given to determine if there is a net force.

____4) Newton's First Law of Motion states that an object at rest stays at rest unless acted upon by a force and an object in motion remains in that motion (unchanged) unless acted upon by a force. Which of the following is not an example of Newton's First Law of Motion? A) An ice skater glides along the ice (frictionless) at a constant speed. B) A basketball is tossed up between two players for the tip-off. It slows down as it move up, momentarily stops, and then speeds up as it falls back down. C) A strong wind blows across the backyard, but your trampoline sits motionless. D) All of these examples demonstrate Newton's First Law.

____5. Newton's Second Law of Motion states that the force (in Newtons, N) an object experiences is proportional to its acceleration (in m/s/s). The proportionality constant is the object's mass (in kg). Written as an equation, Newton's Second Law is F = ma. What is the acceleration that a 0.16 kg baseball hit with a 320 N force experiences? A) 1000 m/s/s B) 2000 m/s/s C) 3000 m/s/s D) 4000 m/s/s

____6. Newton's Third Law of Motion states that for every force there is an equal and opposite reaction force. Which of the following examples could be used to explain Newton's Third Law?

A) When you push on the wall, the reaction force is provided by the wall pushing back on you. B) When you walk, you move your foot in a motion to slide it backwards, and the frictional force between your shoe and the floor is the reaction force that makes you move forward. C) There is a force exerted on the Earth that is equal to force that the Earth exerts to keep the moon in orbit. D) All of these systems describe action-reaction pairs consistent with Newton's Third Law.

____7. You and your chair exert a force of 680 N on the floor. What is the magnitude of the force that the floor is exerting on you and your chair? A) 340 N B) 680 N C) 68 N D) You need more information to answer this question.

____8. Two football players make contact while trying to move in opposite directions. Player A pushes his cleats into the ground making a 50 N force in the forward direction. Player B is pushing on player A with 60 N trying to back player A up. What is the net force on Player A? A) 10 N, backwards

B) 10 N, forwards C) 10 N, but you cannot determine whether he is accelerating forwards or backwards D) 50 N, forwards

____9. One of the following graphs shows an object at rest; two of the graphs show an object moving at a constant speed; and one graph shows an object experiencing an acceleration. Select the correct

connection between the graphs and the behavior of the object. (4 points)

Place an “X” to indicate the correct description for each object:At Rest Constant Velocity Accelerating

Graph AGraph BGraph CGraph D

Newton’s First Law of Motion

An object at rest remains at rest, or if in motion, remains in motion at a constant velocity unless acted on by a net external force

.

There are two experiments to observe at this station.1. Place the block on your table at rest. Now, push the block across the table carefully

observing its motion when you first make contact and once you are no longer touching it.  Your hand provides a net external force.

2. Place the wooden block on the table cloth and then quickly pull the fabric horizontally.

Write a brief paragraph explaining the block’s behavior in these two experiments with respect to Newton’s First Law.

Newton’s Second Law of Motion

a=Fm 

Rearrange the given equation solving for force.

                             F =

Rearrange the given equation solving for mass.

                     m = 

   Complete the following force calculations.  Use 9.8 m/s2 for gravity where needed.

1. A 1250 kg corvette accelerates from rest when the traffic light turns green.  If the corvette is capable of producing an acceleration of 3.00 m/s2, what is the force acting on the car during its acceleration?

A) 420N          B) 3800 N           C) 12000 N D) more information is needed 

2. The net forward force on a 747 airplane is about 800,000 N at take-off.  If the plane accelerates at a rate of 2.0 m/s2, what is the mass of the plane?

A) 80000 kg          B) 1600000 kg         C) 400000 kg D) more information is needed

3. A 4.0 kg bag of apples is hung from a spring scale. Weight is the force of gravity that an object experiences when it is near a planet.  When an object is near the Earth, it will experience an acceleration of approximately 9.8 m/s2 depending on its location (exact distance to the center of the Earth).  What is the weight of the bag of apples? 

A) 39 N          B) 250 N           C) 390 N D) more information is needed 

4. What is the acceleration of a hummingbird that is caught in a wind gust that produces a force of 12 N on the 0.062 kg bird?

A) 0.61 m/s2          B) 74 m/s2           C) 190 N       D) more information is needed 

 

  

Newton’s Third Law of MotionEvery action has an equal and opposite reaction force.

car pulls         truck pullson truck            on car

You have likely seen a tow truck pulling a vehicle down the road.  And, you feel confident that the tow truck must exert a force on the car to make it go.  The car is broken and cannot go on its own, so the truck pulls it along the road.

It may not be as obvious that the car is also pulling on the truck. A quick “thought” experiment to help you see this is to imagine the tow truck pulling a heavier car. As the car gets heavier, the truck would have to pull harder to achieve the same motion.  You could insert yourself into this problem imagining you are pulling someone in a wagon.

                Using a spring scale (or force probe), have one group member hold the spring scale while another group member pulls on the hook.  As the person pulls, the reading on the spring scale shows that the force magnitude increases. The person holding the spring scale also has to increase the force they provide to keep the spring scale from moving.

In order to “see” that both group members are providing a force, repeat the procedure above but hook two spring scales together.  Pull on the system and record the force on each scale (it should be approximately the same. While keeping one scale at rest, have one partner pull harder.  What happens to the reading on the scales?

Now, hold a tennis ball in your hand.  When the ball is at rest, you are providing the reaction force to gravity pulling the bottle down (the ball’s weight). 

If the force that you provide exceeds the weight, the ball will (accelerate up, stay at rest, OR accelerate down).

If the force that you provide is less than the bottle’s weight, the bottle will (accelerate up, stay at rest, OR accelerate down).

With Newton’s Third Law in mind, answer the following true/false questions:1. Action-reaction pairs always act on two different objects.2. When the catcher stops a pitch in his mitt, he exerts a greater force on the ball than the

ball exerts on him.3. A skydiver has had her parachute open for several seconds, and she is falling at a

constant speed.  Her speed is constant because the force of gravity is exactly balanced by the force of air resistance on the parachute.

4. Your windshield hits a bug while you are driving on the highway.  The force on your windshield is exactly the same as the force on the bug.

Newton’s Laws: student responses              Name ____________________

Newton’s First Law of Motion: An object at rest remains at rest, or if in motion, remains in motion at a constant velocity unless acted on by a net external force.

Write a brief paragraph explaining the block’s behavior with respect to Newton’s First Law.

Newton’s Second Law of Motion: a=Fm 

Rearrange the given equation solving for force.

                             F =

Rearrange the given equation solving for mass.

                     m = 

ANSWER(A, B, C or D)

PROBLEM NUMBER GIVEN INFORMATION SHOW YOUR WORK

1

2

3

4

Newton’s Third Law of Motion: Every action has an equal and opposite reaction force.If the force that you provide exceeds the weight, the ball will (accelerate up, stay at rest, OR accelerate down).

If the force that you provide is less than the bottle’s weight, the bottle will (accelerate up, stay at rest, OR accelerate down).

PROBLEM NUMBER 1 2 3 4

TRUE (T) or FALSE (F)

Name _______________________________  Period ______

For each situation, circle the appropriate answer to indicate which of Newton’s Laws of Motion is demonstrated.

For the same force delivered by the engine, a Volkswagen bug can accelerate faster than a cement truck.

1st  2nd 3rd

You fill a balloon with air and then release it. The balloon flies around the room.

1st    2nd 3rd

You roll down a hill at constant speed on your skateboard.

1st          2nd 3rd

Library books sitting on a shelf.1st          2nd 3rd

As you swim in the pool, you push on the water and water pushes you forward.

1st      2nd 3rd

The force required to achieve that same acceleration for a ping pong ball is less than the force to achieve the same acceleration for than a baseball.

1st       2nd 3rd

When jumping on a trampoline, you exert a downward force on the mat and the mat exerts an upward force on you.

1st     2nd 3rd

A skydiver floats to the ground once the upward force of air resistance balances the downward force of gravity.

1st          2nd 3rd

Name(s) _____________________________________________

LAB: Newton’s Laws of Motion

Purpose:  To explore Newton’s Laws of Motion.

Part I:  Newton’s First Law states that an object at rest will stay at rest unless acted upon by a force, and an object in motion remains in motion (constant velocity) unless acted upon by a force.  Complete the following table with your observations of the behavior of the air puck(s).

Situation Set-Up Observations

Attach an inflated balloon to an air puck and place the puck on a flat surface.

Did the air puck move around on the table or did it remain in basically the same position?  [If it moved significantly, make sure the surface is level.]

Re-inflate the air puck, and place it on the table. Quickly, but gently, tap the air puck with a horizontal force from your finger.  

Describe the motion of the air puck.  What made it move from its original position?  What stopped that motion? Include a comment on the role that friction plays in this motion.

Using one or two air pucks, create and observe a situation that you design.  Include a sketch of the step-up and an explanation of the 1st law concept that you are trying to demonstrate.

Part II:  Newton’s Second Law states that the acceleration of an object is the force applied to the object divided by the object’s mass.

Procedure:1. Tighten the pulley clamp onto the edge of your lab bench or table.2. Place one cart across the bench as far from the pulley as possible with the second cart

hanging over the edge.  Make sure that the string is in the groove on the pulley.3. Release the hanging cart.4. Record your observations in the table below.

What happened to the cart on the bench when the hanging cart was released?

What caused the cart to accelerate?  Be specific.

Draw a force diagram for the cart on the bench.

Draw a force diagram for the hanging cart.

Using the additional weights provided, describe how to increase the acceleration of the cart on the bench.  Test your experiment and discuss the results.

Using the additional weights provided, describe how to decrease the acceleration of the cart on the bench.  Test your experiment and discuss the results.

Part III:  Newton’s Thid Law states that forces exist as action-reaction pairs. 

Action-reaction pairs act on each object in the force interaction.  A tow truck exerts a forward force on a car, and the car pulls the tow truck backward with an equal and opposite force.

Another example of an action-reaction pair is demonstrated by a rocket being accelerated forward by hot gas being ejected in the opposite direction.

Figure 11

Using a balloon on a string, the action-reaction pair in which a balloon is thrust forward by air ejected from the balloon can be observed.

Figure 21

Blow up your balloon rocket to about ⅔ full; do not tie the balloon shut.  Referring to the diagram above, tape your rocket to the fishing line track and release it.  Complete the following table.

Record your observations from the time you release the balloon rocket until it stops.

If your rocket did not travel the full length of the track, what should you do so that the rocket travels farther?

What would happen if you added cargo to your rocket?  Why?

Field versus Contact ForcesMagnetic, Electrostatic, and Gravitational Forces

Magnetic Force: Like poles of a magnet (N-N or S-S) repel while unlike poles attract (N-S).The picture (left) shows iron filings along the magnetic field lines of a bar magnet. Iron is used because it can easily become magnetic when placed in the presence of a magnetic field.

FILL-IN RESPONSES OR CIRCLE A CHOICE IN PARENTHESES ON THE STUDENT SHEET TO COMPLETE THIS PAGE (questions are in bold here and provided on the student handout).

1. Place one bar magnet on the table.  Slowly bring a second bar magnet near the first one so that like poles approach each other.  What does the magnet on the table do?  Did the magnets touch each other? (If you did make contact, repeat the experiment to make sure that contact is necessary.)

 2. Repeat step one but bring opposite poles together.  What does the magnet on the table do?  Did

the magnets touch each other?

3. Now, let’s analyze this motion even more carefully. If the magnet on the table was at rest and then it moved, it accelerated.  Acceleration occurs when a force acts on an object. If the magnetic force was the same but the mass of the magnets increased, the acceleration would be (reduced, greater).  You could simulate the magnet being heavier by pressing it down with your finger.  Repeat this experiment a couple times starting with a light pressure and increasing for each trial.  Eventually, you may provide enough force (the magnetic would be so heavy) that the magnetic force interaction would not be sufficient to move it.

 4. Bring the two magnets near one another as shown. Slowly move Magnet B towards Magnet A; stop

moving magnet B when Magnet A begins to move.                                            Magnet A                                               Magnet B

The magnet A does not move until the moving magnet is fairly close. The magnetic force of a bar magnet is a (long or short) range (contact or field) force.

5. Now, repeat the procedure above, but “chase” Magnet A to move it at a constant velocity.  The magnetic force must be equal and opposite the (weight, frictional force) acting on Magnet A.

6. Use one of the bar magnets to pick-up a paper clip.  Explain what you observe including a force diagram for the paper clip.  Would your magnet pick up a piece of paper? Why or why not?

Field versus Contact ForcesMagnetic, Electrostatic, and Gravitational Forces

Electrostatic Force: Atoms are made up of charged particles, and there is a force interaction between charged particles (like charges repel and unlike charges attract).

FILL-IN RESPONSES OR CIRCLE A CHOICE IN PARENTHESES ON THE STUDENT SHEET TO COMPLETE THIS PAGE (questions are in bold here and provided on the student handout).

1. There is a force interaction between objects based on the charge of the object.  A charge may be placed on an object when it is rubbed. For example, you may have noticed your comb has a static charge after running the comb through you hair, and a few strands of hair are attracted to the comb. Or, you may have received a static charge shock when you touch a doorknob after walking across the carpeted floor.  When two objects with like charges (+ and + OR - and -) are near one another, the charges repel each other. If the charges are different (+ and -), the charges attract each other.  

Rub an inflated balloon with the fur (similar to running a comb through your hair).  Now, hold the balloon above some scraps of notebook paper lowering the balloon until the paper moves.  Describe the motion of the paper?  Why do you think the paper moved?

2. Electrostatic forces result from the interaction of the charged particles that make up atoms. Rubbing the balloon with fur removes electrons from the fur giving the balloon a negative charge.  This charge is able to attract the small bits of the paper. The paper is able to respond so that an opposite charge on the paper is (attracted, repelled) by the balloon.

3. Could the negative charge on the balloon pick up a magnet?  As you think about this answer, perhaps you think that the magnet is simply too heavy?  Or, is there no interaction between the charged balloon and the magnetic field? Could the balloon pick up a much lighter paper clip?  Why or why not? Write a short paragraph to respond.

4. Investigate the interaction between two balloons rubbed with fur.  Electrostatic force is a (long or short) range (contact or field) force.

5. What happens to the interaction between the two balloons after a few minutes?  Why do you think this change happens? Write a short paragraph to respond.

6. Tear off a piece of tape about five inches long.  Press the tape onto your lab bench leaving a tab at one end.  Holding this tab, quickly remove the tape from the bench, turn the tape over (sticky side up) and bring the tape near the bench where it had been stuck to the surface.  What do you observe and why? Write a short paragraph to respond.

Field versus Contact ForcesMagnetic, Electrostatic, and Gravitational Forces

Gravitational Force: The universal law of gravitation tells us that there is an attractive force between any two objects that have mass.  For masses of common objects, like you and your physics book, this attractive force is so small that you do not observe it.  But, when looking at the system of you and the Earth, this force of attraction keeps you on the surface of the planet. You are actually being accelerated toward the center of the Earth.  And, the Earth is accelerating toward you! (Newton’s Third Law action-reaction force pair)

1. Hold a tennis ball approximately shoulder high.  Release the ball and observe what happens. Why does the ball fall down (toward the center of the Earth)?

 2. When objects are in free-fall, they are experiencing a force interaction with the Earth.  If you consider the

mass and radius of the Earth to be approximately constant values, the value of the acceleration of gravity is g = 9.8 m/s2. Since all objects that are near the Earth experience the force of gravity, this force has a special name; it is called weight.  Using Newton’s Second Law, F = ma, the equation to calculate the weight of an object is W = mg. A student’s mass is 48 kg.  What is his weight?

If you were to climb a tall mountain and increase the distance you are from the center of the Earth (effectively increase the radius of the Earth), the acceleration of gravity would have a lower value.   

3. When a rocket is launched into space, it takes a tremendous force to make the rocket “escape” Earth’s gravitational force acting on objects near the planet.  When you throw a ball upward, you can make it go higher and higher by throwing it harder and harder, but you cannot get the ball high enough to become weightless (escape Earth’s gravitational force).  Think about the NASA missions to the moon. The moon also has a large mass compared to the rocket, so there would be an attractive force pulling on an object near the moon.

Since the moon’s mass is less than the Earth’s mass, the spaceship would be (not quite halfway or passed halfway) on its mission to the moon when the moon’s gravitational pull was greater than the Earth’s gravitational pull. 

4. True or false:  When the spaceship landed on the moon, the Earth’s gravitational force on it became zero?

5. Gravitational force is a (long or short) range (contact or field) force. 

Contact versus Field Forces                          Name ____________________

FILL-IN RESPONSES OR CIRCLE A CHOICE IN PARENTHESES ON THE STUDENT SHEET TO COMPLETE THIS PAGE. 

Magnetic Force: 

1. What does the magnet on the table do?  Did the magnets touch each other?

2. What does the magnet on the table do?  Did the magnets touch each other?

3. If the magnetic force was the same but the mass of the magnets increased, the acceleration would be (reduced, greater).

 4. The magnetic force of a bar magnet is a (long or short) range (contact or field) force. 

5. The magnetic force must be equal and opposite the (weight, frictional force) acting on Magnet A.

 6. Explain what you observe including a force diagram for the paper clip.  Would your magnet

pick up a piece of paper? Why or why not? 

Electrostatic Force: 

1. Describe the motion of the paper?  Why do you think the paper moved?

2. The paper is able to respond so that an opposite charge on the paper is (attracted, repelled) by the balloon.

3. Write a short paragraph to respond.

4. Electrostatic force is a (long or short) range (contact or field) force.

5. Write a short paragraph to respond.

6. Write a short paragraph to respond.

Gravitational Force: 1. Why does the ball fall down (toward the center of the Earth)?

2. A student’s mass is 48 kg.  What is his weight? 

3. Since the moon’s mass is less than the Earth’s mass, the spaceship would be (not quite halfway or passed halfway) on its mission to the moon when the moon’s gravitational pull was greater than the Earth’s gravitational pull. 

4. True or false:  When the spaceship landed on the moon, the Earth’s gravitational force on it became zero?

5. Gravitational force is a (long or short) range (contact or field) force. 

Field versus Contact ForcesForce as an Interaction

DIRECTIONS

Examine the pictures and description of the system. 

Complete the Field versus Contact by CIRCLING the correct descriptors about the force shown and sketching the force diagram.

Two balloons, each with a net positive charge, repel each other.

An ocean-going ship floats on the water.

Adam pushes the box to the right sliding the box across the rough floor.

The top pair of magnets repel each other, and the bottom pair of magnets attract each other.

The chandelier hangs from the ceiling by four chains.

The moon orbits the Earth approximately every 27 days.

The hammock is connected to the trees with two ropes.

This man stands on his bathroom scale.

Name(s) _____________________________________________            Period _______

Field versus Contact Forces

DIRECTIONS

Examine the pictures and description of the system. 

Complete the Field versus Contact Forces STUDENT HANDOUT by CIRCLING the correct descriptors about the force shown and sketching the force diagram.

Field OR ContactForce diagram (both balloons): Field OR Contact

Force diagram (ship):

Field OR ContactForce diagram (box):

Field OR ContactForce diagram (top pair magnets):

Field OR ContactForce diagram (chandelier):

Field OR ContactForce diagram (Earth and moon):

Field OR ContactForce diagram (hammock):

Field OR ContactForce diagram (person):

Name(s) _____________________________________________            Period _______Field versus Contact

Circle the correct force type and sketch the force diagram for each picture.

balloons: FIELD or CONTACT force

Force diagram of two balloon system. (horizontal forces only)

chandelier: FIELD or CONTACT force

Force diagram of the chandelier.

ship: FIELD or CONTACT force

Force diagram of the ship.

moon: FIELD or CONTACT force

Force diagram of the moon.

box: FIELD or CONTACT force

Force diagram of the box.

hammock: FIELD or CONTACT force

Force diagram of the hammock.

magnets: FIELD or CONTACT force

Force diagram of each pair of magnets.

person on scale: FIELD or CONTACT force

Force diagram of the person.

Questions for class discussion: A rubbed balloon will pull a student’s hair toward the balloon and make contact even though electrostatic force has been identified as a field force.  Magnetic force has also been identified as a field force. Is there a force between two magnets that are in contact? Extend this discussion to include the Earth’s gravitational force acting on you.

                  Name(s) _____________________________________________

LAB: Weight, Normal, Applied and Frictional Force

Purpose:  To explore different types of forces and the role each plays in the motion of an object.

A force is defined as an interaction between two objects.  A common example is two teams playing tug-of-war. The members of one team pull on the rope trying to pull the entire opposing team across the finish line or sometimes into a mud pit.  At one moment, the teams are pulling equally in opposite directions, and the rope is at rest. Then, one team wants the win, so they count down and pull with a burst of force. This winning team exerts on the rope is sufficient to accelerate the losing team.  When thinking about everyday life, there are many times an object is pushed or pulled to cause its motion to change.

When the motion of an object is analyzed, a force diagram is drawn to identify the interactions which are used to determine the acceleration of the object.  When balanced forces are present, the net force is zero, and the acceleration of the object is also zero. When the net force is not zero, either because a single force is acting or the collection of forces acting does not add to zero.  The object accelerates in the direction of the net force. In this lab, you will accelerate a wooden block across your lab bench by pulling on the spring scale as shown here.

An object has mass (measured in kilograms).  When this object is near a larger mass, like the Earth, there is an interaction between the two masses which is called the object’s weight (measured in Newtons).  Weight is calculated by multiplying the mass times the acceleration of gravity (on the surface of the Earth, g = 9.8 m/s2.  The vector arrow for weight on the force diagram is drawn straight down to indicate this interaction pulls the object toward the center of the Earth.  Label the weight vector on the diagram below.

When drawing the force diagram, think of only the object, or in other words, imagine that the block is no longer in contact with the table.  To show the table-block interaction on the force diagram, there is an upward vector arrow representing the table “holding the object” up preventing gravity from accelerating it down.  If the upward force (or table) were not there, the block would be in free fall. This force acts up from and perpendicular to the table’s surface; it is called the normal force. Label the normal force on the diagram below.

Place the spring scale hook through the loop on the block and put the spring scale to the right of the block as shown.  Keeping the spring scale horizontal, pull the spring scale gently to the right until the block moves. This force is an example of an applied force or an interaction between your pulling and the block.  Label the applied force on the diagram below.

The final force to analyze is the force of friction.  The normal force (block/table interaction) supported the block with a perpendicular force.  The frictional force is also an interaction between the block and table, but the frictional force acts parallel to the contact surfaces and acts opposite the applied force.  Label the applied frictional force on the diagram below.

In order to increase the frictional force, place the sandpaper side of the block down and place the two 50 g masses on the block.  Attach the spring scale and slowly pull on the block taking note of the force being measured by the spring scale. You may have to repeat this process several times watching the spring scale carefully.  Then, circle one of the choices in the bold parenthesis) in the lines below to analyze the motion of the block.

First, consider the two forces acting in the vertical direction.  The block is (at rest OR moving) vertically even while you pull on it.  The block remains vertically at rest because the net force acting in the vertical direction is (non-zero OR zero).  The vertical forces are balanced.  Another way of stating that fact is that the normal force is (less than, equal to, OR greater than) the weight.

When the applied force is zero, the block remains at rest.  In this situation, the applied force is (less than, equal to, OR greater than) the frictional force, and both of these forces are zero.  As you begin gently pulling on the block, the applied force increases.  If the applied force is non-zero and the block remains at rest, then the frictional force must (be zero OR be equal and opposite to the applied force.)

Once the applied force is greater than the maximum force that friction can provide, the block (remains at rest OR accelerates).  The applied force and the frictional forces are unbalanced.  The net force accelerates the block in the direction of the applied force.

Repeat the experiment with the sandpaper block and no weights.  The applied force needed to pull the block is (greater OR less) than the applied force needed when the weights were present.  What measurement confirms this is true?

Repeat the experiment three times with the two weights in place: 1 - sandpaper block, 2 - block with mirror/glass, and 3 - two wooden blocks.  Rank the blocks from the set-up with the most friction (requires greatest applied force to move) to the least friction (requires least applied force to move).

Most friction Least friction

Write a brief paragraph explaining your results.

Conclusion:

Name __________________________________  Period ___________

Draw and analyze the force diagram for each case presented. Determine the net force acting as indicated.

The tow rope begins to pull you along level ground with a force of 120 N while the frictional force acting on your skis is 80 N.

Force Diagram:

Net Force:

Waiting for your friend to get into the canoe first you provide a 225 N force to hold the canoe at rest against the current.

Force Diagram:

Net Force:

You hang a 250 kg weight from the spring scale and hold it steady while your lab partner records the reading on the scale.

Force Diagram:

Net Force:

Continuing to hold the spring scale, you think it is starting to slip from your hand.  You jerk it upward providing an additional 550 N force upward.

Force Diagram:

Net Force:

A hot air balloon pilot fires her burner to produce an upward force 1200 N.  The pilot and the balloon have a weight of 1200 N. The wind is blowing to the east and exerts a 400 N force on the balloon.

Force Diagram:

Net Force:

You and your teammate both kick the soccer ball at the same time.  You provide a 72 N force to the north while your teammate provides a 24 N force to the south.

Force Diagram:

Net Force:

Interpreting Graphs1. Determine the mass of the object which was

used to make the following graph.        The object mass is ____________.

 

2. Indicate the times on the following graph [place the appropriate letter in each box below the curve] when (a) the object was moving faster and faster (accelerating in the positive direction) and     (b) the object was moving slower and slower (force acting opposite the direction of motion).

3. Label each line with the appropriate mass:  Object A = 2.0 kg, Object B = 4.0 kg, and Object C = 8 kg. [Enter a1, a2, or a3 on the appropriate line.]

Y-axis label given in legend.

Object A is graph ______.

Object B is graph ______.

Object C is graph ______.

4. Which line on the graph indicates the presence of air resistance?

[Enter graph 1 or graph 2.]

Air resistance is present in ____________.

5. This graph shows the speed of a car moving down the road after the light turns green.

[Give the time or time range that matches each of the following descriptions.]

During what time(s) is the car experiencing balanced forces? ________________

During what time(s) is the car experiencing unbalanced forces and speeding up?

________________

During what time(s) is the car experiencing unbalanced forces and slowing down?

_________________

At what time(s) is the car at rest? _________________Forces - Final Assessment            Name ____________________________  Period ______

Using the word bank at the bottom of this section, complete each statement with the correct term

____1. The ______ of an object is the same on every planet in the solar system.

____2. As a block slides across the concrete sidewalk,  ______ opposes the motion of the block and concrete surfaces that are in contact.

____ 3. When an object moves at a constant velocity, the net force is zero.  Another way of stating that the net force is zero is that the forces are ______.

____4. The mass of an object times the acceleration of gravity is called the object’s ______.

____5. If you were to travel to a mountaintop, your weight would ______.

____6. When the motion of an object changes direction, it had to experience a ______.

____7.  As you accelerate from rest when a traffic light turns green, there is a net forward force acting on you.  Another way of describing this motion is that the velocity ______.

____8. The direction of the net force gives the direction in which the object will ______.

____9. When the north pole of one bar magnet is brought near the south pole of another magnet, the magnets attract each other.  This is an example of a ______ force.

____10. In order to get snacks up to their tree house, a rope is tied to a bucket and raised.  The tension (force) in the rope is an example of a ______ force.

a) accelerate e) field i) non-zero force

b) balanced f) friction j) unbalances

c) contact g) increases k) weight

d) decrease h) mass l) zero net force

____11.  While driving down the highway at 70 miles per hour, a large bug hits your windshield.  Which of the following statements correctly describes the force interaction between your car and the bug.a) The car and the bug experience the same force. This situation is an example of Newton’s Third Law.b) The car does not experience a force from the bug. This situation is an example of Newton’s First Law.

c) The bug has a very small mass, so it does not experience a force.  This situation is an example of Newton’s Second Law.d) The bug experiences a greater force.  This situation is an example of all three of Newton’s Laws.

____12.  Two objects of roughly the same size are dropped.  One, a rock, hits the ground before the other, a ping-pong ball.  The rock hits the ground first because

a. gravity pulls harder on the rock.b. the greater mass of the rock allows it to cut through the air easier.c. the lower density of the rock makes it go faster.d. ping-pong ball is too light to interact with the Earth.

____13. There is a tennis ball laying at rest in the bed of a pick-up truck.  The driver accelerates when the light turns green, and the ball remains at rest (appears to move toward the back of the truck).  Which of the following does this example demonstrate?

a. Newton’s First Lawb. Newton’s Second Lawc. Newton’s Third Lawd. Conservation of Mechanical Energy

____14.  A 0.450 kg baseball is hit with a force of 90.0 N.  What is the acceleration of the ball?a.  40.5 m/s2          b) 162 N           c) 200. N d) 500. N

____15.  When an object is in free-fall, the Earth pulls on it, anda. the object’s speed is constant.b. the object pulls on the Earth.c. the object’s inertia increases.d. the Earth’s pull is less than the pull of the moon on the object.

____16. An object experiencing a non-zero net force (unbalanced forces)a. is always falling toward the center of the Earth.b. has a constant velocity.c. has an acceleration equal to zero.d. accelerates in the direction of the net force.

____17.  Complete the concept map describing characteristics of force.

Use the following to fill in the answers to A - E.

air resistance

electrostatic

frictional

gravitational

magnetic

A ________________________

B ________________________

C _______________________

D _______________________

E _______________________

____18.  The frictional force acting between two surfaces increases for          a) surfaces that are very smooth            b) surfaces that have little contact between them          c) surfaces with increased roughness          d) surfaces that are covered with ice.

____19.  Two dragsters line up to race each other.  The motion of the dragsters when the light turns green is graphed here:

Which of the lines represent the car that accelerates at a greater rate.          a) Dragster A accelerates at a greater rate.           b) Dragster B accelerates at a greater rate.          c) The dragsters accelerate at the same rate.          d)  There is not enough information on the graph to answer this question.

____20.  Select the diagram(s) that is(are) consistent with a net force of zero.

The wind blows against the balloon with a force of 17 N.

A

The resistive force of moving through the water exactly matches the wind force making the sailboat move at a constant speed.

B

The dog pulls on the toy with a force equal to the force that the owner pulls. The toy remains at rest.

C

                        a) only A          b) only B c) only C          d) B and C