NEWTON’S LAWS OF

MOTION Forces

1st Law of Motion

2nd Law of Motion

3rd Law of Motion

Force: a push or a pull on an object

*Force is measured in Newtons*

Forces

Balanced and Unbalanced Forces

- Balanced forces - forces that are equal but in

opposite directions, canceling each other.

- Unbalanced forces – forces that are unequal, one

is greater than another; a change in motion will

result

- Net Force - the combination of all forces acting on

an object

50N 50N

Forces

Identifying forces:

Forces

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

• Potential energy = stationary.

Where is Potential Energy the greatest?

Where is Kinetic Energy the greatest?

NEWTON’S

LAWS OF

MOTION

1. Is this magic or is this real and can be explained with science?

2. How did it work?

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?

Read pages 51-52 (stop at Second Law of Motion)

and fill in your 1st Law Notes

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

Inertia Depends on Mass

For your notes:

- the 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.

Newton’s 1st Law (aka Law of Inertia)

- Did it really work?

- Why?

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

from moving.

- Inferring Why should the girl use a slippery tablecloth?

- Would heavy dishes or light dishes work better?

Newton’s 1st Law (aka Law of Inertia)

NEWTON’S LAWS OF

MOTION 2nd Law of Motion

3rd Law of Motion

What will happen?

VS

Result?

What will happen?

Result?

VS fast slow

What will happen?

VS

Result?

• 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?

Read pages 52 – 54 (start at Second Law of Motion) and fill in your 2nd law notes

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

its mass and the 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

Newton’s 2nd Law of Motion

• What if mass is 10 kg and acceleration is 7

m/s2?

F = MA

F = 10 kg x 7 m/s2

F = 70 N

Newton’s 2nd Law of Motion

Newton’s 2nd Law of Motion What about acceleration due to gravity?

If dropped at the same time, would a hammer and feather fall at the same speed?

What about on the Moon? Yes, there is still gravity 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. On Earth though, we have air resistance.

• 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

Newton’s 2nd Law of Motion

- If you and your friend are both on skates and

you push on each other.

- Sitting in a kayak you take a paddle and push

against the water.

- You hit a volleyball.

So you’re saying that for every force there is an

equal and opposite force?

Read pages 55-57 and fill in your 3rd Law notes.

What will happen?

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?

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

force does the golf ball put back on the club?

- 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)?

- If you drop a bowling ball on the ground what is the reaction of

the Earth? Why?

Newton’s 3rd Law of Motion