1. FORCES

2. Isaac Newton Lived 1642-1727 Mathematician, Physicist, Astronomer
LAWS of Motion
Law of Universal GRAVITATION
Development of Calculus

3. Newton’s 1st Law
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
Key idea: INERTIA

4. Inertia Tendency of an object to resist a change in motion
As mass INCREASES inertia increases
 mass =  inertia
As mass DECREASES inertia decreases
 mass =  inertia
Ex: A big truck has more inertia than a small car. More inertia makes it more difficult for the big truck to start moving, stop moving, or CHANGE DIRECTION

5. Friction A force that works against motion
Makes objects slow down, stop or stay still

6. Example: While riding a skateboard (or wagon or bicycle), you fly forward off the board when hitting a curb, a rock or another object which abruptly halts the motion of the skateboard

7. Do not let this be you! Wear your seat belt!
If no force acted on a body it remains at rest OR continues motion along a straight line with constant speed
Do not let this be you! Wear your seat belt!
Because of inertia, objects (including you) resist changes in their motion. When the car going 80 mph is stopped by the brick wall, your body keeps moving at 80 mph.

8. Newtons 2nd Law
The acceleration of an object depends on the mass of the object and the amount of force applied
Describes the motion of an object when an unbalanced force acts on the object

9. Expressing 2nd Law Mathematically
The relationship of acceleration (a) to mass (m) and force (F) can be expressed mathematically:
F = m x a
m = F / a
a = F / m

10. Acceleration Depends on Mass
The acceleration decreases as its mass increases
The acceleration increases as its mass decreases
mass & acceleration are indirectly proportional

11. Mass Depends on Force
An object’s mass increases as the force on the object increases.
An object’s mass decreases as the force on the object decreases.
Mass and force are directly proportional. Double the mass you double to force to move the object.

12. Force and Acceleration
The direction of the acceleration of an object is always in the direction of the force (push or pull)

13. Example
What is the acceleration of a 3 kg mass if a force of 15 N is used to move the mass?
(Note: 1 N is equal to 1 kg x m/s2)

14. Example
Suppose you are pushing an empty cart. You have to exert only a small force on the cart to accelerate it. But, the same amount of force will not accelerate the full cart as much as the empty cart.

15. Example
Suppose you give the cart a hard push. The cart will start moving faster than if you gave it only a soft push. The cart will move forward because the push was in the forward direction.

16. Newton’s 3rd Law
For every action there is an equal and opposite reaction.
These forces can be balanced or unbalanced.
Unbalanced forces will result in movement.

17. Balanced forces are all around us!
Anything that has mass (everything) will exhibit a force on anything touching it.
If an object is at rest, then the force it has on other objects is equal to the forces they have on it.

18. What does this mean?
The giant boulder exerts a force of 900 N on the ground underneath it.
Why doesn’t the boulder fall through the Earth?
The ground exerts a counter force of 900 N back onto the boulder, in the opposite direction.

19. Even things in motion follow Newton’s 3rd Law:
A bird flies by use of its wings.
The wings of a bird push air downwards.
The air must also be pushing the bird upwards.
The size of the force on the air equals the size of the force on the bird
The direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards).
Action-reaction force pairs make it possible for birds to fly.

20. EXIT TICKET: Summarize each law in 1-2 sentences. Use your OWN WORDS.
You should have 3-6 sentences total for your summary.
TURN IN YOUR NOTES W/ SUMMARY
I will return these to you tomorrow.