1. Newton’s Laws of Motion
Forces
Table of Contents
Newton’s Laws of Motion

2. Essential Question: How Do Objects React to Forces?
What is Newton’s First Law of Motion?
What is Newton’s Second Law of Motion
What is Newton’s Third Law of Motion

3. Vocabulary
Inertia-resistance to change in motion Inertia movie

4. Newton’s Laws of Motion
First Law An object in motion will stay in motion, and an object at rest will stay at rest unless an unbalanced object acts on it. Second Law An object that has an unbalanced force acting on it will accelerate in the direction of that force (an object’s acceleration depends on its mass and on the net force acting on it) Third Law Forces always occur in equal and opposite pairs (one object exerts (applies) force on another object, then the second exerts equal strength in the opposite direction on the object) Action pairs= Action force & Reaction force

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1st Laws of Motion

6. Newton’s First Law of Motion
If an object is not moving, it will not start moving until a force acts on it. If an object is moving, it will continue at a constant velocity until a force acts to change its speed or direction. Newton’s 1st law of motion states that an object at rest will remain at rest unless acted upon by an unbalanced force. An object moving at a constant velocity will continue moving at a constant velocity unless acted upon by an unbalanced force.

7. Newton’s First Law of Motion
Inertia-resistance to change in motion
Inertia depends on Mass
Some objects have more inertia than others
The greater the mass of an object
greater inertia (resistance to change motion)
The greater the force required to change its motions
Fig. 1

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2nd Laws of Motion

9. Newton’s Second Law of Motion
An object that has an unbalanced force acting on it will accelerate in the direction of that force
(an object’s acceleration depends on its mass and on the net force acting on it)

10. 2nd Law of Motion
If two dogs are on each side, then the total force pulling to the left (200 N) balances the total force pulling to the right (200 N). That means the net force on the sled is zero, so the sled doesn’t move.

11. Acceleration Equation: Acceleration = Net Force Mass Net Force Equation: Net Force = Mass X Acceleration

12. Newton’s Laws of Motion
Newton’s Second Law
Suppose that four dogs pull a sled carrying two people. How can the pictures be completed to represent answers to the two different questions?

13. Assess your understanding
DO THE MATH
Every year in cities around the world, teams create cars, push them across platforms, and hope they will fly. Unfortunately, the cars always end up accelerating down into the water.
Calculate- If a 100-N net force acts on a 50 kg car, what will the acceleration of the car be?_______________________
Calculate- After the car leaves the platform, gravity causes it to accelerate downward at a rate of 9.8 m/s2. What is the gravitational force on the car?
________________________________________________
Assess your understanding

14. (kg•m/s²)= Newton S.I. Unit for Acceleration = M/s2
S. I Unit for Mass= kg
S.I. Unit for Force= N
Newton’s 2nd Law of Motion- Force is measured in kilograms times meters per second per second
(kg•m/s²)= Newton
force is measured This unit is also called the newton (N), which is the SI unit of force.
One Newton is the force required to give a 1kg mass an acceleration of 1 m/s2

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3rd Laws of Motion

16. Action force & Reaction force
3rd Law of Motion
Third Law
Forces always occur in equal and opposite pairs
(one object exerts (applies) force on another object, then the second exerts equal strength in the opposite direction on the object)
Action pairs=
Action force & Reaction force .
Another way to state Newton’s third law is that for every action there is an equal but opposite reaction. Action and reaction forces do not necessarily cancel out because they may act on different objects

17. 3rd Law of Motion
Sir Isaac Newton's Third Law of motion, which states that for every action, there is an opposite reaction.
The classic example is air rushing out of a balloon (action) and the balloon streaking ahead (reaction).
r. pg. 344

18. DID YOU KNOW?
Newton’s 3rd law of motion explains why rockets accelerate in space, even though there is no water or air to push off of. Inside rockets, gas is produced. When the rockets push that gas backward out of the rocket, a reaction force occurs that pushes the rocket forward.

19. Newton’s Laws of Motion Action-Reaction Forces
How can the illustration of the dogs be completed to represent Newton's Third Law of Motion?

20. What Makes a Bug Go Splat?
Newton’s Laws of Motion
What Makes a Bug Go Splat?
Splat! A bug
has just flown into the windshield of an oncoming car. The car
must have hit the bug much harder than
the bug hit the car, right?