Newton’s Laws of Newton’s Laws of MotionMotion

Question #1 – just think about Question #1 – just think about it, don’t write it down.it, don’t write it down.

A bus driver slams on his brakes. All A bus driver slams on his brakes. All of the backpacks on the floor slide of the backpacks on the floor slide forward. Why does this happen?forward. Why does this happen?

Newton’s First Law: The Law of Inertia An object in motion will stay in motion and an

object at rest will stay at rest…until an outside force acts on it.

Definition of Inertia: An object’s resistance to a change in motion.

Mass is the measure of Inertia

Weight is a Force

The force with which an object is attracted toward a celestial body (earth, moon, sun, etc…) by gravity.

Difference Between Mass Difference Between Mass and Weightand Weight

MassMass the measure of the measure of inertia.inertia.

The mass of an object The mass of an object does not change does not change based on it’s locationbased on it’s location

10kg on the moon is 10kg on the moon is 10kg on Earth.10kg on Earth.

WeightWeight is a force. is a force.

A 75 kg man weighs A 75 kg man weighs around 160 lbs. on around 160 lbs. on Earth. He is still 75 kg Earth. He is still 75 kg on the moon, but he on the moon, but he weighs 27 lbs. on the weighs 27 lbs. on the moon because the moon moon because the moon is smaller and has less is smaller and has less of a gravitational pull.of a gravitational pull.

Whiplash

Inertia in Photography A screwdriver was

dropped on a water balloon and for a moment after the balloon broke away the water maintained the same shape.

Which has more mass? The balloon or the water?

Which resisted a change in motion more? The balloon or the water?

What is a Force?

Definition of Force

A force is a push or pull that causes an object to accelerate.

Newton’s Second LawNewton’s Second Law

Force = Mass x AccelerationForce = Mass x Acceleration

F = ma

Units of Force

Forces are measured in units called “Newtons” (N)

A 20 N Force is required to accelerate a 10kg ball by 2m/s

2

F = ma F = 10(2) = 20 N

Use “g” when dealing with gravityUse “g” when dealing with gravity

F = mgF = mg

This is the equation to find the force of This is the equation to find the force of gravity pulling on an objectgravity pulling on an object

g = 10 m/sg = 10 m/s22

FrictionFriction• Friction is a force that occurs when two objects come in contact with one another. It is like a “sticky” force

•Friction causes moving objects to slow down, and therefore accelerate, so it is a force

•Even very smooth objects are rough at a microscopic level. This roughness is what causes friction.

Newton’s Third (and final) Law of Newton’s Third (and final) Law of Motion: Action-ReactionMotion: Action-Reaction

When one object exerts a force on a When one object exerts a force on a second object, the second object second object, the second object exerts an equal force in the opposite exerts an equal force in the opposite direction back onto the first objectdirection back onto the first object

Sometimes stated “every action has Sometimes stated “every action has an equal and opposite reaction.”an equal and opposite reaction.”

FF1 1 = -F= -F22

If the mass is big, If the mass is big, the acceleration is the acceleration is small. If the mass small. If the mass is small than it has is small than it has a greater a greater acceleration.acceleration.

mA =MamA =Ma

Newton’s 3Newton’s 3rdrd Law is Why Guns Law is Why Guns Have RecoilHave Recoil

Recoil is the force felt Recoil is the force felt by a shooter from the by a shooter from the gun as it is fired. gun as it is fired.