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Newton’s Laws of Motion

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Newton’s Laws of Motion

Chapter 19 Forces

Section 3 pg 739

Section 4 pg 743

- Born & studied in England
- One of the most influential scientists of all time
- His discoveries of forces led to his credit of the Newton.

Main Idea: Newton’s Laws of Motion

- First Law of Motion
- Second Law of Motion
- Net Force = Mass X Acceleration
- Third Law of Motion
- Review Notes
- Discuss Homework for next class

- Also known as The Law of Inertia
- Inertia has a 2 part definition:
Part I: If an object is moving, then it will continue to move until a force stops it.

Part II: If an object is at rest, then it will remain at rest until a force moves it.

- Mass: the amount of matter in an object. The measure of mass does NOT change if gravity is not present.
- Greater Inertia:
The more mass an object has the harder it will be to move or keep still.

- Less Inertia:
The opposite is true: If an object has less mass, then it will be easier to move or keep still.

- Ask yourself, which one has the greater mass? The lesser mass?
- Also, based on your guesses about mass, which one has the greater inertia? Lesser inertia?
- The strength of inertia is directly proportional to the mass of the object.
- In other words, what happens to mass also happens to inertia.

- Newton’s First Law of Motion
*The more mass an object has, the more inertia it will have

*The less mass an object has, the less inertia it will have

Remember objects with more mass are always harder to keep still or keep moving! This affects how much inertia an object has.

- Main Idea of this Law: It’s a math problem
- Law States…
Net Force = Mass X Acceleration

Let’s test out this formula…

Ex 1: What is the net force on a 1,000 kg object accelerating at 3 m/s2?

1: What formula will you use? NF = M X A

2: Plug in the values. NF = (1,000kg)(3 m/s2)

3: Solve! Net Force = 3,000 Newtons

- Ex 2: A car speeds up as it moves along the road. If a force of 175 N is needed to make the car accelerate to 25 m/s2. What’s the car’s mass?
- Formula: Net Force = Mass x Acceleration
- OR Mass = Net Force / Acceleration
- Plug in your values: Mass = 175 N / 25 m/s2
- Divide and your answer is a MASS OF IS 7 kg

- Calculate the amount of acceleration needed to move a 25 kilogram statue with a force of 75 N.
Formula: Acceleration = NF / Mass

Plug in values A = 75 N / 25 kg

Divide and your answer is A = 3 m/s2

- Cause: This means an action that happens
- Effect: This is what happens as a reaction to the cause
- If your good friend beats you at video games, then you will smack that person with the nearest pillow.
- In this case what’s the cause? The effect?

“ Newton’s Third Law of Motion states that 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.”

What????

- For every action, there is an equal but opposite reaction.
- Forces react to each other in opposite ways.
- That’s why this law is cause and effect!