Newton’s Laws of Motion

In this PPT

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Some Vocabulary…

Weight – how strong gravity is pulling on youGravity – a pull towards the center of an object

On Earth, the pull on an object towards the center of the Earth

The more mass an object has, the stronger the pull of gravity.The Earth has a gravitational pull 6 times greater

than that of the moonJupiter has a gravitational pull 2.4 times greater than

that of Earth

Gravity and Weight

Mr. Albano’s weight on Earth is ~60kg.What is his weight on the moon?What is his weight on Jupiter?Does his mass change on the moon? On

Jupiter?

Newton’s First Law of Motion

An object in motion stays in motion unless acted on by an unbalanced force

An object at rest (not moving) will stay at rest unless acted on by an unbalanced force

Newton’s First Law of Motion

Also known as the Law of InertiaInertia – The reason an object stays at rest, or

in motion

Newtons’s 1st Law and You

Don’t let this be you. Wear seat Don’t let this be you. Wear seat belts.belts.

Because of inertia, objects Because of inertia, objects (including you) resist changes in (including you) resist changes in their motion. When the car going their motion. When the car going 80 km/hr is stopped by the brick 80 km/hr is stopped by the brick wall, your body keeps moving at 80 wall, your body keeps moving at 80 km/hr.km/hr.

Newton’s First Law

“Rounding” CornersCan you run around the desk without slowing

down?

“Rounding” Bases

Another Inertia Example

I’m safe over here. That guy is toast!

Stay over there, you’ll

be safe!

Hehehe

More Inertia

“Red Light / Green Light”

“Weightlessness”

Without friction, Newton’s 1st Law is perfectExample – Outer Space

How a shuttle orbitsWeightless = Falling???

GRAVITY

Forward Inertia

Parabolic Flight (Projectile Motion)

Projectile Motion

Projectile - object thrown or launched and does not move under its own power

The combination of initial forward velocity and the downward force of gravity causes things to travel in a curved path (parabola) Ex: throwing a ball, a ski jump, a cannon ball being shot, punting a football

If it wasn’t for gravity, the ball would continue to travel in a straight line due to Inertia

Videos

1st Law – NFL2nd Law - NFL3rd Law - NFL

Newton’s 2nd Law of Motion

Newton’s 2nd Law

Force = mass x acceleration

Acceleration = The rate something speeds up, or slows down

Force – let’s review!

How hard something is pushing or pulling

Measured in “Newtons” (N)

Ex. I pushed the ball up the hill with 10 N of force

Units for 2nd Law Problems

For our purposes, we will only be using the following units (standard SI units) when solving Newton’s 2nd Law related problems:FORCE = Newtons (N)MASS = kilograms (kg)ACCELERATION = m/s/s (meters per second

per second)

F = m x a

What happens to the force if:You increase the acceleration?You increase the mass?

Examples

Two students are in a baseball game. The first student hits a ball very hard and it has a greater acceleration than the second student who bunts the ball lightly.

A soccer ball accelerates more than a bowling ball when thrown with the same force.

Example 1 – Prove it mathematically!

Two students are in a baseball game. The first student hits a ball very hard and it has a greater acceleration than the second student who bunts the ball lightly.

Baseball has a mass of 0.15kg.

Student A hits very hard with a Force of 1000N

Student B bunts with a Force of 100N

a = F ÷ mStudent A

a = 1000 ÷ 0.15 = 6666.67 m/s/sStudent B

a = 100 ÷ 0.15 = 666.67 m/s/s

Example 2 – Prove it mathematically!

A soccer ball accelerates more than a bowling ball when thrown with the same force.

Soccer ball mass = 0.5kgBowling ball mass = 6.5kgForce = 50NSoccer ball

a = 50 ÷ 0.5 = 100 m/s/sBowling ball

a = 50 ÷ 6.5 = 7.7 m/s/s

Newton’s 2nd Law proves that different masses accelerate to the earth at the same rate, but with different forces.

Objects that are falling accelerate to the ground at the same rate (9.8 m/s/s) When the upward force of air resistance = the downward force of gravity pulling on the object, it stops accelerating.

We call this Terminal Velocity

However, because of the 2nd Law we know that they don’t hit the ground with the same force.

Objects that are falling accelerate to the ground at the same rate (9.8 m/s/s) When the upward force of air resistance = the downward force of gravity pulling on the object, it stops accelerating.

We call this Terminal Velocity

However, because of the 2nd Law we know that they don’t hit the ground with the same force. F = maF = ma

98 N = 10 kg x 9.8 m/s/s98 N = 10 kg x 9.8 m/s/s

F = maF = ma

9.8 N = 1 kg x 9.8 m/s/s9.8 N = 1 kg x 9.8 m/s/s

Can a cat survive a fall from a plane?

There’s another reason besides a cat’s natural instincts to detect acceleration…

Cat’s average mass = 9 kgHuman’s average mass = 75 kgAcceleration due to gravity = 9.8 m/s/sWho hits the ground with more FORCE?

Example:

A boulder has a mass of 8 kg, and you push it so that it accelerates 3 m/s/s. How much force did you push it with?

Example:

You push your friend in the next desk with a force of 18 Newtons. They have a mass of 2 kg. How much will they accelerate?

Example:

Your parents ask you to help the neighbors move. They ask you to pull a box into the truck. You pull with exactly 35 Newtons of force, and the box accelerates 5 m/s/s. What was the mass of the box?

Newton’s 3rd Law of Motion

Newton’s 3rd Law

Every action has an equal and opposite reaction

Example:Action = You kick a soccer ballReaction = The soccer ball kicks you!

In other words…

“This means that for every force there is a reaction force that is equal in size, but opposite in direction. That is to say that whenever an object pushes another object it gets pushed back in the opposite direction equally hard.”

Examples

Fish through water - water goes back, fish goes forward

Bird flying - wings push down, air pushes up

Fire hose - water comes out, hose pushes back

Balloon

Rocket Example

The rocket's action is to push down on the ground with the force of its

powerful engines, and the reaction is that the ground pushes the rocket

upwards with an equal force.

Gravity Example

More Examples

Space shuttle lifting off

Airplane flying through the air

EVERY force has a reaction force