EQ: What is the relationship

between force and

acceleration? Pg. 19

Newton’s First Law(law of inertia)

An object at rest tends to stay at rest and an object in motion tends to stay

in motion unless acted upon by an unbalanced force.

http://www.sciencechannel.com/games-and-interactives/newtons-laws-of-motion-interactive.htm

Newton’s First Law (law of inertia)

• INERTIA is a property of an object that describes how ______________________ the motion of the object

• more _____ means more ____

much it will resist change to

mass inertia

Balanced Force

Equal forces in opposite directions cancel out.

Object in motion will stay in motion.Object at rest will stay at rest.

Unbalanced Forces

Unequal opposing forces produce an unbalanced forcecausing change in motion

(acceleration- change in velocity)

If objects in motion tend to stay in motion, why don’t moving objects keep moving

forever?

Things don’t keep moving forever because there’s almost always an unbalanced force

acting upon them.

A book sliding across a table slows down and stops because of the force of friction.

If you throw a ball upwards it will eventually slow down and fall because of the force of gravity.

1st Law

• Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

1st Law

• Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction) it would never stop!

Inertia

Closing Task:Clearing up those misconceptions with a

shoulder partner

1. A force is needed to continue the objects motion

2.There are no forces in outer space

3. Acceleration is velocity or acceleration is speeding up

Closing Task:Clearing up those misconceptions with a

shoulder partner1. Misconception - A force is needed to continue the objects motion

An object can fly through space with a constant velocity as long as no external forces act on it (unbalanced force).

2. Misconception – There are no forces in spaces

A spaceship can be accelerated if acted upon an external force (example: a meteor hits the ship, fuel gives ship more power to accelerate)

3. Misconception – Acceleration is velocity or acceleration is speeding up

Acceleration is a change in velocity (speeding up, slowing down, stopping, changing direction)

Newton’s Second Law

The acceleration of an object as produced by a net force is directly proportional to the magnitude of

the net force, in the same direction as the net force, and inversely proportional to the mass of the

object.Fnet = m • a

The acceleration of an object as produced by a net force is directly proportional to the magnitude of

the net force, in the same direction as the net force, and inversely proportional to the mass of the

object.Fnet = m • a

http://www.sciencechannel.com/games-and-interactives/newtons-laws-of-motion-interactive.htm

Fnet = m • a

Newton’s Second Law

Quantity Variable Unit

Force F Newtons (N)

Mass m Kilograms (kg)

Acceleration a meters/second2 (m/s2)

• WEIGHT is a measure of the force of ________ on the mass of an object

measured in __________

Calculate your weightMass = pounds/2.2

Ex: 130 lbs/2.2 kg = 59 kg

F = ma

F = (59 kg)(9.80 m/s2)

F = 578 ~ 580 N

gravity

Newtons

Newton’s Second Law

Remember, acceleration of gravity, a=g= 9.80 m/s2

Newton’s Second Law

A house is lifted from its foundations onto a truck for relocation. The house is pulled upward by a net force of 2850 N. This force causes the house to move from rest to an upward speed of 0.15 m/s in 5.0 s. What is the mass of the house? 

Newton’s Third Law

For every action there is an equal and opposite reaction.

Newton’s Third Law

• A bug with a mass of 5 grams flies into the windshield of a moving 1000kg bus.

• Which will have the most force?

• The bug on the bus• The bus on the bug

Newton’s Third Law

• The force would be the same.

• Force (bug)= m x A

• Force (bus)= M x a

Think I look bad?You should see the other guy!

If mass remains constant, doubling the acceleration, doubles the force. If force remains constant, doubling the mass, halves the acceleration.

3rd LawThe reaction of a rocket The reaction of a rocket is an application of the is an application of the third law of motion. third law of motion. Various fuels are burned Various fuels are burned in the engine, producing in the engine, producing hot gases. hot gases.

The hot gases push The hot gases push against the inside tube of against the inside tube of the rocket and escape out the rocket and escape out the bottom of the tube. the bottom of the tube. As the gases move As the gases move downward, the rocket downward, the rocket moves in the opposite moves in the opposite direction.direction.

Consider hitting a baseball with a bat. If we call the force applied to the ball by the bat the action force, identify the reaction

force.

(a) the force applied to the bat by the hands

(b) the force applied to the bat by the ball

(c) the force the ball carries with it in flight

(d) the centrifugal force in the swing

(b) the force applied to the bat by the ball

Pause it:talk about these misconceptions with a

shoulder partner1. Objects with more mass “push harder” than objects with less mass.

2. Objects with more mass experience greater gravitational acceleration than objects with less mass.

Newton’s 3rd Law

• Suppose you are taking a space walk near the space shuttle, and your safety line breaks. How would you get back to the shuttle?

Newton’s 3rd Law

• The thing to do would be to take one of the tools from your tool belt and throw it is hard as you can directly away from the shuttle. Then, with the help of Newton's second and third laws, you will accelerate back towards the shuttle. As you throw the tool, you push against it, causing it to accelerate. At the same time, by Newton's third law, the tool is pushing back against you in the opposite direction, which causes you to accelerate back towards the shuttle, as desired.

What Laws are represented?

ReviewNewton’s First Law:

Objects in motion tend to stay in motion and objects at rest tend to stay at rest unless acted upon by an unbalanced force.

Newton’s Second Law:

Force equals mass times acceleration (F = ma).

Newton’s Third Law:

For every action there is an equal and opposite reaction.

Group WorkWrite up:

•Is it possible for you to continue sliding across a surface if all forces are balanced? Explain

•What could you do to minimize the acceleration of an object if something was to bump into you? Hint, think of F = ma

•You walk into a pole while texting on your phone, which object experienced the bigger force? Which object experienced the greater acceleration?