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NEWTON’S

LAWS OF

MOTION

Potential vs. Kinetic Energy • Kinetic energy = moving energy. Increases with

speed.

• Potential energy = stationary. Increases with

height.

Where is Potential Energy the greatest?

Where is Kinetic Energy the greatest?

Balanced and Unbalanced Forces

- Balanced forces - forces that are equal but in

opposite directions, canceling each other.

- Unbalanced forces - if one force is greater than

another, a change in motion will result

- Combining forces – the combination of all forces

acting on an object is called a NET FORCE

- *Force is measured in Newtons*

50N 50N

Forces

Identifying forces:

Forces

Hammer and Feather on the Moon?

At the end of the last Apollo 15 moon walk (July 1971),

Commander David Scott held out a geologic hammer

(1.32-kg aluminum) and a feather (0.03-kg falcon feather)

and dropped them at the same time. Because they were

essentially in a vacuum, there was no air resistance and

the feather fell at the same rate as the hammer, as Galileo

had concluded hundreds of years before - all objects

released together fall at the same rate regardless of mass.

http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_15_feather_drop.html

http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_15_feather_drop.html

What will happen? - Clothes on the floor of your room.

- A ball rolling across the gym floor.

- A tennis ball flies through the air after you hit it.

- The car you are riding in suddenly stops.

- You left your sonic drink on the roof of the car

and the driver stomps on the gas.

- The driver of the car takes a sudden turn.

So you’re saying that the objects at rest stay at rest, the

moving objects stay moving and they also resist changing

their motion?

Newton’s 1st Law of Motion An object at rest will stay at rest unless acted on by an

unbalanced force, and an object in motion will stay in

motion unless acted on by an unbalanced force.

For your notes:

- Newton’s 1st Law - An object at rest will stay at rest, an

object in motion will stay in motion unless acted on by an

unbalanced force.

• Whether an object is moving or not, it resists any change

to its motion. Galileo’s concept of the resistance to a

change in motion is called inertia.

For your notes:

- Inertia is the tendency of an object to resist a change in

motion.

Newton’s 1st Law of Motion

Newton’s 1st Law (aka Law of Inertia)

Inertia says that objects at rest want to stay at rest and objects in motion want to stay in motion – they resist changing motion.

You move forward in your seat when a car stops suddenly. When the car stops, inertia tried to keep you moving forward. A force, such as the pull of a seat belt, is required to change your motion.

Furthermore, objects want to remain in motion in a straight line. This means that objects want to resist changes in speed or direction.

When a car is turning a corner, a driver’s body is usually thrown outward causing them to shift in their seat. This shift of the pull outward is due to inertia.

Inertia The inertia of the objects on the table keeps them from

moving.

Inferring Why should the girl use a slippery tablecloth?


Inertia Depends on Mass

Newton noticed a special relationship between the mass and the inertia of an object. He concluded that more the mass an object has, the more it resists a change in motion (more mass = more inertia).

For example: Which is harder to move?

An adult on a swing vs. a small child

Why?

An empty aquarium vs. one full of water

Why?

The greater the mass of an object is, the greater its inertia, and the greater the force required to change its motion.

add to notes under inertia


• Two trucks are traveling at the same speed towards each other. If truck A is big and it runs into small truck B, in what direction does small truck B go?

• A bouncy ball is thrown at a window and a baseball is thrown at a window both are thrown at the same speed. Which one will do more damage?

• You’re walking down the hallway and someone walks into you when you turn a corner. The next day the same person is running down the hall and runs into you when you turn the corner. Which day does it hurt more?

So, you’re saying that force depends on how big something is or how fast it’s moving?

What will happen?

Newton’s 2nd Law of Motion The acceleration of an object depends on the object’s mass

and on the net force acting on the object.

For your notes:

- Newton’s 2nd Law - acceleration of an object depends on

it’s mass and force acting on it.

Force = Mass x Acceleration

Newton’s 2nd Law of Motion

• Force is measured in Newtons (N)

• Acceleration is measured in meters per second squared

(m/s2)

• Mass is measured in kilograms (Kg)

For your notes:

Force – Newtons (N)

Mass – Kilograms (Kg)

Acceleration – meters per second squared (m/s2)

• If mass equals 200 kg and the acceleration

equals 3 m/s2 you can plug these into the

equation F = MA. It would look like this:

F = MA

F = 200 kg x 3 m/s2

F = 600 N


• What if mass is 10 kg and acceleration is 7

m/s2?

F = MA

F = 10 kg x 7 m/s2

F = 70 N


• If a 30 kg sand bag is dropped from a hot air

balloon, what will its force be when it hits the

ground? (the acceleration of gravity is 9.8 m/s2)

F = MA

F = 30 kg x 9.8 m/s2

F = 294 N


- If you and your friend are both on skates and

you push on each other.

What will happen?



- Sitting in a kayak you take a paddle and push

against the water.

What will happen?



- Sitting in a kayak you take a paddle and push

against the water.

- You hit a volleyball.

What will happen?

So you’re saying that for

every force there is an

equal and opposite

force?

Newton’s 3rd Law of Motion If one object exerts a force on another object, then the

second object exerts a force of equal strength in the

opposite direction on the first object.

For your notes:

- Newton’s 3rd Law – for every action there is an equal and

opposite reaction

- If a tennis racket hits a tennis ball with a force of 2,500 N, what

force does the tennis ball put back onto the racket?

Newton’s 3rd Law of Motion



- If a golf club strikes a golf ball with a force of 9,000 N, what

force does the tennis ball put back on the club?






- Why is the golf ball deformed in this picture?






- Why is the golf ball deformed in this picture?

- If the forces are equal then why doesn’t the a baseball bat fly

as far as the baseball (in the opposite direction)?


- All 3 laws are at work all the time. We can apply all 3 laws

to one situation:

Newton’s 3 Laws of Motion

Some aid organizations, like the Red Cross,

deliver supplies to hard to reach people by

parachuting them down.

1. What forces are working on the parachute?

2. Draw AND label those forces.

3a. Is the object accelerating?

3b. Why or why not?

4. The supplies and parachute have a mass of

3,000 kg. Before the parachute was opened

is was accelerating at 9.8 m/s2. If the

parachute had failed, what would have been

the force the supplies would have hit the

ground with?

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