physics unit - mrs. shaw - homeshawj.weebly.com/.../section_1_notes_-_student_notes.docx · web...

asddas

Section 1

Physics Unit

Section 1.0

1.1 Motion

1.2 Velocity

1.3 Acceleration

1.4 Work and Energy

Each section will have a number of different topics with practice problems to be completed. Quizzes will be given after two subsections.

Developed 2012

EnergyEnergy is the capacity of a physical system to perform work. Energy is measured in joules (J).

Types of Energy:

----

----

Energy can be transferred from one form to the next.

Example: Solar panels can gather UV rays (solar energy) and can transfer it to electrical energy to light a light bulb (electrical energy) and that light bulb gives off heat (heat or thermal energy)

Example: When eat a sandwich, which gives us energy (chemical energy) and that chemical energy can be transferred to a grumbling in your stomach (sound energy) or to move your arm (mechanical energy) and to keep your body warm (heat or thermal energy).

There are two main forms of energy:- Kinetic energy is

_________________________________________________________o Example: Wind energy – the molecules of gas within the air are

moving giving them kinetic energy

- Potential energy is ______________________________________________________________________________________________________________

o Example: Water stored in a dam for hydroelectricity generation. When valves are opened the force of gravity cause water to begin to flow. The gravitational potential energy of the water is converting to kinetic energy. The flowing water can turn a turbine, which will further convert the kinetic energy of the water into useable mechanical energy. An alternator or generator then converts the mechanical energy from the turbine into electrical energy. This electricity is then sent to the electricity grid and to our homes where it is converted into light energy (lights and televisions), sound energy (televisions, stereos), heat energy (hot water,

Science 10: Physics Unit2

toasters, ovens), mechanical energy (fans, vacuum cleaners, fridge and air conditioner compressors) and so on.

1.1 MotionWe can analyze the motion of an object only if we compare the object’s position to another point.

Example: Floating out in a lake on an air mattress. It doesn’t feel like you are moving but eventually you are out past the buoy.

Motion occurs when ________________________________________________________________________________________________________________________________________________.

Once we know that there is motion we can begin to describe it. In some cases we may only want to know the change in length, other cases only knowing the change in direction. There may also be cases where we want to know the change in both length and direction.

One type of motion is uniform motion. Uniform motion is a term used to describe an object _________________________________________________________________________.

This type of motion is extremely hard to maintain for long periods of time.Example: __________________________________

Example: Even a car that has the cruise control set at 100km/hr does not travel in perfect uniform motion. The car experiences friction on the tires from the road, wind resistance, going up a hill. All of these things make the engine attempt to maintain the set rate but that rate still fluctuates.

True examples of uniform motion are:- artificial satellites moving in circular motion around the earth- the earth moving around the Sun at a speed of 107 000km/hr- the move of the seconds hand on a watch

List a few key points you learned about the MAGLEV train:

-

-

-


Average Speed

As a result of it being extremely difficult for an object to maintain uniform motion the term average speed is usually used. Average speed is _______________________________________________________________________________________________________________. To accurately analyze average speed you need to use mathematical formulas or graphs.

Using Formulas to Analyze Average Speed

average speed=distance travelledtime elapsed

v=∆d∆ t

v=d final−d initialt final−t initial

Example Problem:A person walks 10.0m away from a stop sign in 5.00s. What is the average speed of the person?

v=∆d∆ t

¿ 10.0m−0.0m5.00 s−0.00 s

¿ 10.0m5.00 s

¿2.00 msThe person walked at a speed of 2.00 m/s

Practice Problems: See attached sheet “Speed Worksheet”Science 10: Physics Unit4

Using Graphs to Analyze Average Speed

A graph is an important tool in analyzing uniform motion because it shows two things:

- a relationship between two variableso You can compare distance versus time

- a visual representation of the motiono You can see if a person walking stopped at any point in the journey

Two types of graphs that can be used are:

-

-

Plotting Distance-Time Graphs

Example: A motorboat is travelling at uniform speed. The boat passes marker buoys placed 5m apart, which act as a measuring scale. As the boat passes the first marker, a person on shore starts to record the distance the boat travels away from the first marker every 2.0s.


Timet (s)

Distance from first markerd (m)

0.0 0

2.0 10

4.0 20

6.0 30

8.0 40

10.0 50

0 2 4 6 8 100

10

20

30

40

50

60

Distance-Time Graph of Boat

Time t (s)

Dis

tan

ce d

(m

)

In the graph we can see the line of best fit. The _____________________________________ is a straight line drawn through the center of various points on a scatter plot. In this example the line of best fit connects our points and has a positive slope. This indicates a direct linear relationship between the distance travelled and the time taken to travel the distance. This means as the time increases the distance increases. The graph also shows that the motorboat has uniform motion. As long as the line is a straight line, the object represented in the graph is displaying uniform motion. If the line of best fit were a curve of any type this would mean that the object was changing distance travelled in equal time intervals, meaning it would be either speeding up or slowing down.

The _______________ of the line in the graph above tells us something about the motion.

slope= riserun

slope= change∈distancechange∈time = ∆d∆ t

slope=∆d∆ t = speed

slope = speedv=∆d

∆ t

¿ 30m−10m6.0 s−2.0 s


¿ 20m4.0 s

¿5.0 ms

Therefore the average speed, v, is 5.0m/s.

The slope of a distance time graph is a visual representation of the speed of an object. A greater or steeper slope indicates a faster speed and a lesser indicates a slower speed.

Practice Problem: See attached sheet “Suzette’s Run”Plotting a Speed-Time Graph

Using the same motorboat example as before, let suppose that there is a person on shore with a radar gun. They use the radar gun to record the speed of the motorboat every 2.0s.

Science 10: Physics Unit

Line 2

Line 3

Line 1

Distance d(m)

Time t(s)

Describe the motion of the objects represented by the three lines.

7

Timet (s)

Speed of the boat passing

each markerv (m/s)

0.0 5.00

2.0 5.00

4.0 5.00

6.0 5.00

8.0 5.00

10.0 5.00

0 2 4 6 8 100

1

2

3

4

5

6

Speed-Time Graph of Boat

Time t (s)

Sp

eed

v (

m/s

)

This graph also describes the motion of the motorboat. The line of best fit indicates a linear relationship between speed and time elapsed. The line is horizontal, which means that as the time elapsed increased, the speed remained constant. This confirms that the boat has uniform motion.

A calculation also confirms uniform motion:

slope= riserun

=∆ v∆ t

¿ 5.00m/ s−5.00m/ s10.0 s−0.0 s

¿ 0.00m /s10.0 s

¿0.0 ms2

A slope of 0.0m/s2 confirms that the motion is uniform. The slope of a speed-time graph is ___________________________. If there is no acceleration it means we have ___________ ________________________.

You can determine the ____________________ the boat travelled by calculating the area under the line on a speed-time graph.

area under the line = area of a rectangle = length X width


Time t(s)

Speed v(m/s)

Line 1

Line 3

Line 2

area = (v)(∆ t) = (5.00m/s)(10.0s – 0.0s) = (5.00m/s)(10.0s) = 50m

Since the speed formula ( v=∆d∆ t ), can be rearranged to (v)(∆ t)=∆ d, the area under the line is the same as ∆ d.

If the line of best fit were a straight line with a slope other than zero then the line would represent an object that is changing its ________________. From the slant of the sloe of the line on a speed-time graph you can tell whether the speed of the object is ______________________________________________________________.

1.2 VelocityWe learned in the previous topic that speed describes the rate of motion of an object. What then is velocity? Velocity describes ___________________________________________ _____________________________________________________.


Describe the motion of the objects represented by the three lines.

9

Example: To determine the speed of a car you can look at the speedometer but to determine the velocity of the car you need to look at the speedometer and a compass.

The difference between speed and velocity is that speed is a scalar quantity and velocity is a vector quantity.

A scalar quantity –

A vector quantity –

A vector quantity is written with a vector arrow above the symbol for the measured quantity. For example the symbol for speed is v, and the symbol for velocity is v⃑. Distance and displacement are another example of scalar and vector quantities. Distance is a scalar quantity. It measures the change in distance of an object moving from a starting reference point.

Diagram 1

Example: A person moves from the bus stop to a point 10m away from it. You would record the distance the person moved as ∆ d = 10m.

_____________________________ is a vector quantity and measures the change in distance and the direction or the change in position of an object from a reference point. To determine displacement you need to know both the beginning and final positions and the direction moved.

Example:In Diagram 1 you can record the displacement as d⃑= 10m (right). This indicates that the person ends up 10m from the reference point. It also indicates that the direction of travel was to the right of the reference point.


Diagram 2

Diagram 2 illustrates an important difference between distance and displacement. The distance (∆ d) is the total distance travelled by the person on both sides of the bus stop. So ∆ d is 8m. The displacement (∆⃑ d) is the person’s change in position relative to the bus stop. So ∆⃑ d is 2m (left).

How to Identify Vector Directions

Vector directions can be described using one of two ways:- the X-axis method- the navigator method

The X-axis method uses the mathematical coordinate system with an x-axis and a y-axis.


Direction given along the x-axis and y-axis are as follows:

-

-11

Direction given along the axis lines have positive or negative values:

-

-

- Directions between the axis lines are given in degrees and are not give a positive or negative value.

North (0°)

The navigator method uses the directions of north, east, south, and west on a grid to identify vector directions.

Speed and Velocity

Both distance travelled and speed are ___________________ quantities. Only the magnitude of each one is stated. Both displacement and velocity are vector quantities therefore you must state both the magnitude and the direction.

average velocity=displacementtime elapsed

v⃑ ¿ ∆⃑ d∆ t

= d⃑ final−d initialt final−t initial


Direction given along the x-axis and y-axis are as follows:

-

-

Right (0°)

12

Example:A person walks 10.0m [E] away from the bus stop in 5.00s. What is the average velocity of the person?

v⃑ ¿ ∆⃑ d∆ t

= 10.0m [E ]−0.0m5.00 s−0.00 s

= 2.00m/s [E]The person walked at an average velocity of 2.0m/s [E].

Using Graphs to Analyze Average Velocity

To analyze average velocity you can use two types of graphs:-

- Position-Time Graph

Going back to the motorboat example, suppose that the motorboat is travelling east pas six marker buoys in the water each placed 10.0m apart. A person on shore is recording when the motorboat passes each buoy.


0 2 4 6 8 100

10

20

30

40

50

60

Position-Time Graph of Boat

Time t (s)

Pos

itio

n d

(m

)

13

Marker

Time

t (s)

Position of the boatd⃗ (m)

1 0.0 0.0

2 2.0 10.0

3 4.0 20.0

4 6.0 30.0

5 8.0 40.0

6 10.0 50.0

The line of best fit indicates a linear or straight-line relationship between the position and the time taken to travel. This means as time increases the position also increases. The straight line of the graph shows that the motorboat’s displacement in relation to the time interval is constant. Therefore the motorboat is moving with uniform motion. Its velocity remains constant. You can use the slope of the line to determine the average velocity of the motorboat.

slope= riserun

= change∈ positionchange∈time

= velocity

v⃑ ¿ ∆⃑ d∆ t

= 40.0m [E ]−10.0m[E]8.0 s−2.0 s

= 5.0 m/s [E]

Velocity-Time Graph

Keeping with the motorboat example, suppose the motorboat is travelling east at uniform velocity pas six marker buoys 10.0m apart. On shore one person is measuring the time using a stopwatch, and another is using a radar gun and using a compass to determine direction.


The average velocity of the motorboat is 5.0m/s [E].

0 2 4 6 8 100

10

20

30

40

50

60

Position-Time Graph of Boat

Time t (s)

Pos

itio

n d

(m

)

14

Time 0 2 4 6 8 100

1

2

3

4

5

6

Velocity-Time Graph of Boat

Time t (s)

Vel

ocit

y v

(m

/s)

[E]

The line of best fit is a straight line. This indicates a linear relationship between the velocity of the boat and the time it took to travel past the markers. The line is also horizontal which means that the velocity remained constant during the time the motorboat was moving past the markers. The boat is travelling at a uniform motion.

Assignment: Comparing Velocity and Speed/ Distance and Displacement


Marker

Time

t (s)

Velocity of the boatv⃗ (m/s) [E]

1 0.0 5.0

2 2.0 5.0

3 4.0 5.0

4 6.0 5.0

5 8.0 5.0

6 10.0 5.0

Quiz

1.3 AccelerationUp until now we have been discussing uniform motion. Although understanding uniform is essential for this physics unit in the real world uniform motion is rather boring. Think of the coin operated horse at IGA. That horse moves forward and back at a uniform motion. This ride is not one that we get particularly excited about. This next video helps introduce our next topic, a more “exciting” type of motion.

Video Clips

The factor that makes the rollercoaster ride and the car ride exciting is the topic we are now going to explore; acceleration.

Acceleration is_____________________________________________________________________. Although uniform motion is the simplest type of motion, accelerated motion is the most common type of motion. Similar to velocity, acceleration is a vector quantity and thus you must determine both the magnitude and direction. Depending on what is occurring with the magnitude and direction will determine the type of acceleration.

Types of acceleration:- Positive acceleration- Negative acceleration

Depending on the direction of travel and whether or not we are experiencing positive or negative acceleration will determine if we are speeding up or slowing down.

Speeding up:


a

v When our velocity is positive and our acceleration is positive, the object is _________________________.

Example: Putting a car in drive and pressing the gas pedal.

16

The best way to think of acceleration being positive or negative is to think of it the same way as direction. Up, north, right and east are positive for acceleration whereas down, south, left, west are negative.

Example:http://www.physicsclassroom.com/mmedia/kinema/avd.gif

Bungee Cord Example:Think of those big bungee cords that are attached to you. You are running one direction, say to the right, so you velocity is to the right. Because the bungee cord is attached to you however, the acceleration is in the opposite direction, to the left. This difference in direction causes you to slow down.

In other words, when the magnitude of the velocity and the direction are both positive or both negative, acceleration is positive. When magnitude of velocity and the direction are opposite, acceleration is negative. We call positive acceleration speeding up whereas negative acceleration we say is slowing down.


a

v When our velocity is negative and our acceleration is negative, the object is_______________________________.

Example: A bungee jumper falling before he reaches the bottom of his jump.

a

vWhen our velocity is positive and our acceleration is negative, the object is ____________________________________.

Example: A car travelling east at a constant velocity and then the driver presses the brake pedal.

a

v When our velocity is negative and our acceleration is positive, the object is _____________________________________.

Example: A new driver is back up at a constant velocity and hits the gear shift knocking the car into drive. The switch from reverse to drive will slow you down momentarily.

17

http://www.physicsclassroom.com/mmedia/kinema/avd.gif

Analyzing Accelerated Motion

As with uniform motion, you can study accelerated motion by using formulas and graphs.

acceleration= change∈velocitytimeinterval

a⃑ ¿ ∆⃑ v∆ t

= v⃑ final−v initialt final−tinitial

Example: A racing car accelerates from rest to a speed of 55.6m/h [E] in 6.00s. What is the acceleration of the car?

a⃑ ¿ ∆⃑ v∆ t

= 55.6m /s [E ]−0.00m / s6.00 s−0.00 s

= 9.27m/s2 [E]

The car accelerated at a rate of 9.27m/s2 east, which is an example of positive acceleration.

Note: The units for velocity are m/s and the units for acceleration are m/s2.

Plotting a Position-Time Graph


In the previous section we saw that uniform motion produced a line of best fit that was straight. This was because the velocity was uniform. For accelerated motion, the line of best fit is a ________________________________.

The motorboat is travelling with accelerated motion towards east and passes marker buoys placed 5m apart. As the boat passes the first marker buoy a person on shore records the position of the boat every 2s in reference to the first buoy.

0 2 4 6 8 100

5

10

15

20

25

30

Position-Time Graph

Time t (s)

Pos

itio

n d

(m

) [E

]

The graph shows the slope of the line of best fit as gradually increase, which indicates that the velocity of the boat is gradually increasing or accelerating. The shape of the curve of the graph indicated whether there is positive or negative acceleration.


Time t (s)

Position d

Position d

This graph has an increasing slope, which indicates _____________________________________

This graph has a decreasing slope, which indicates __________________________________

Position-Time Graph

Position-Time Graph

19

Timet (s)

Position of the Boatd⃗ (m) [E]

0 0

2 1

4 4

6 9

8 16

10 25

Plotting a Velocity-Time Graph

Again, suppose the motorboat is accelerating headed east. A person on shore used a radar gun and records the velocity of the motorboat every 1.0s, as soon as it passes the first buoy.

0 1 2 3 4 50

2

4

6

8

10

12

Velocity-Time Graph

Time t (s)

Vel

ocit

y v

(m

/s)

[E

]

The line of best fit is a straight line with increasing slope. This indicates that the velocity of the motorboat is increasing with time. The slope of the line of best fit can be calculated as follows:

slope= riserun

¿ ∆⃑ v∆ t since a⃑ ¿ ∆⃑ v∆ t

slope = acceleration

= 10.0m/ s [E ]−0.00m /s5.0 s−0.0 s

= 10.0m/ s [E ]5.0 s


Timet (s)

Velocity of the Boatv⃗ (m/s) [E]

0.0 0.0

1.0 2.0

2.0 4.0

3.0 6.0

4.0 8.0

5.0 10.0

= 2.0 m/s2 [E]The acceleration of the boat is 2.0m/s2 [E].

Velocity-time graphs can show positive or negative acceleration depending on the slope of the line.


Velocity v (m/s)

Velocity-Time Graph

Time t (s)Velocity-Time Graph

Time t (s)

Velocity v (m/s)

This graph represents ________________ acceleration because the slope is increasing.

This graph represents ______________ acceleration because the slope is decreasing.

21

Force 1 Force 2

Force 1 Force 2

Unbalanced forces are not equal in magnitude (force 2 is greater than force 1) or are not in opposite direction. Force 1

Force 2

1.4 Work and EnergyA ball at rest on a billiard table will remain at rest. It does not move because all forces acting on it are balanced. Force is __________________________________________________ __________________________________________________.

What causes the ball to move? The ball will only move when an unbalanced force is applied to it. Once the force acting in one direction is greater than the force in the opposite direction the ball will move.

Once an object is in motion, it tends to remain in motion, moving at a constant speed in a straight line. However, if an unbalanced force is applied to the moving ball, it will either speed up or slow down (accelerate). If the unbalanced force is applied in the same direction as the ball’s motion, the ball will speed up. If the unbalanced force, such as friction between the ball and the table, is applied in the direction opposite to the direction of the ball’s motion, the ball will slow down.


Balanced forces are equal in magnitude (force 1 equals force 2) but opposite in direction, so they cancel each other out.

moving ball speeds upunbalanced force

22

Work

Work is ____________________________________________________________________________ __________________________________________________________

work = force X distance the object travels W = Fdjoule = newton X meter

In physics, work is a very specific term and has a more specific meaning than its everyday meaning. For example, you may think that sitting at a desk studying is doing work. Although this task may be very exhausting in terms of a physical definition, you are not doing work because nothing is moving or changing position.

Three conditions for work to be done on an object:1. There must be movement.

Someone pushing against a wall as hard as they can is not doing any work because the wall does not move.

2. There must be force.A person riding a bicycle that is coasting is not doing any work on the bike even though there is movement. The person is not applying a horizontal force to the bike.

3. The force and the distance the object travels must be in the same direction.A person carrying a backpack is not doing any work on the pack when she is carrying it parallel to the ground because the force of her hand is vertical but the distance the pack is travelling is horizontal.


force

direction

23

The Relationship between Work Output and Work InputWhen a force is applied to move an object through a distance, work is done on the object. This is call work input or energy input. Work input is calculated by the formula W=Fd.

In the absence of any outside forces, such as friction, the total work input should equal the total work output.

Example: A weightlifter lifts a barbell a vertical distance of 2.40m. If the average force required to lift the barbell is 2.00 X 103 N, how much work is done by the weightlifter on the barbell?

W = Fd = (2.00 X 103 N)(2.40m) = 4.80 X 103 J

The work done by the weightlifter is 4.80 X 103 J.

Energy

If a body has energy, then the body can do work by transferring the energy to another object. Energy is____________________________________________________. Work and energy are actually the same thing. If a body does work on an object, then the body doing work loses energy, and the object has work done to it gains energy. For example, a pool cue loses energy as I hits a ball, and the ball once hit gains the energy the cue loses. An energy transfer has occurred and the cue performs work on the ball.

Since work and energy are the same, they have the same units, joules (J).change in energy = work

∆ E= W joules = joules

Quiz


physics unit - mrs. shaw - homeshawj.weebly.com/.../section_1_notes_-_student_notes.docx · web...

Documents