Unit 11: Newton's Laws of Motion

Unit 11: Newton's Laws of Motion

By S Harris

Issac Newton​ was a 22-year-old student at Cambridge University in 1665

• used his free time to develop the law of universal gravitation, calculus, and the 3 laws of motion.

Who is Newton?

States that an object will remain at rest or move in a straight line, at a constant speed, unless acted on by a net outside force

• An object in motion, stays in motion unless another force causes it to stop or forces it to move.

Newton's First Law of Motion

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As you watch the clip, think of 2 cases where you see Newton's 1st Law taking place.

Link to Avengers clip: ​https://youtu.be/PARfU2Vi694?si=de8aUsijAeuH2-A4

Sometimes called the Law of Inertia

• Inertia is the tendency of an object to resist any change in motion (so it will either remain at rest or it will continue moving depending on what it was doing in the beginning)

Newton's First Law of Motion

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Does a bowling ball have the same inertia as a tennis ball?

Question:

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No, an object's inertia is related to its mass. So the bowling ball has greater inertia.

• the greater the mass, the greater the inertia​

Answer:​

The more inertia an object has the more resistance to a change in motion

• (a.k.a: it is harder to move heavier objects)

What does greater inertia mean?

Multiple Choice

If you applied a force of 10 N to both a toy car and a real car, which would have the greater acceleration?

• toy car

• real car

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States that a force on an object is equal to the mass (the amount of matter in an object) times the acceleration of the force acting on it.

• Equation:​

Newton's Second Law of Motion

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​F = mass x acceleration

F = ma​

​F

​m

a

• ​acceleration will decrease as mass increases​ (because it would require a larger force to create the same acceleration on a heavier object.)

What happens to acceleration as mass increases?

​m

a

​F

Multiple Choice

You push a wagon that has a mass of 12 kg. If the net force of the wagon is 6 N south, what is the wagon's acceleration?

• 12 m/s² south

• 0.5 m/s² south

• 6 m/s² south

• Gravity has an acceleration of 9.8 m/s²

  • So to determine the force of an object that is falling you would multiply the object's mass by the acceleration of gravity.

What about gravity?

• A tennis ball is thrown up into the air and falls back to the ground. What is the amount of force the ball will have when it hits the ground if it's mass is 0.057 kg. (acceleration of gravity is 9.8 m/s²)

Example:

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Work:

Multiple Choice

A tennis ball is thrown up into the air and falls back to the ground. What is the amount of force the ball will have when it hits the ground if it's mass is 0.075 kg. (acceleration of gravity is 9.8 m/s²)

• 0.56 N

• 0.74 N

• 0.01 N

• 171 N

states that when one object exerts a force on another object, the second object exerts an equal and opposite force.

• so, "For every action there is an equal and opposite reaction."​

Newton's Third Law of Motion

As you watch the clip, think of 2 cases where you see Newton's 3rd Law taking place.

Link to Avengers clip: ​https://youtu.be/LAkGDL5bvuM

Forces do not always cancel.

• this is because there can be multiple different forces or types acting on objects

  • action and reaction forces act on different objects

Newton's Third Law of Motion