1. Inertia What is inertia?
The tendency of an object to resist change
An object tends to stay still if it’s still, or stay moving if it’s moving
What do you have to do to get something to move?
Overcome inertia; apply an unbalanced force

2. Newton’s Laws of Motion
First Law:
An object in motion stays in motion, unless acted upon by an (unbalanced) net force. It will continue to move at constant speed in a straight line. An object at rest stays at rest, unless acted upon by an unbalanced (net) force.
Newton’s first law is also known as the “Law of Inertia”

6. Newton’s laws of motion
Remember that unbalanced forces cause acceleration (a change in velocity)
What factors determine how much an object will accelerate?
Amount of force, mass, and direction of force

8. What happens if you apply a big force and a small force to the same object?
The big force will accelerate it more

9. What happens if you apply the same force to objects with different masses?
The object with the smaller mass will be accelerated more

10. Newton’s laws of motion
Newton’s Second Law:
Force is related to an object’s mass and acceleration
F = ma
The greater the force, the greater the change in motion

12. Newton’s laws of motion
Third Law:
For every action force, there is an equal and opposite reaction force
Forces always act in pairs
The two forces act in opposite directions.
When you push on something, that is an action force. The object pushes back on you with a reaction force.

13. Action-reaction (Newton’s 3rd law)
When you bounce a basketball, what is the action force?
The ball hitting the floor
What is the reaction force?
The floor pushing back on the ball, causing it to bounce back
What happens when you increase the action force?
The reaction force also increases

14. Action-reaction (Newton’s 3rd Law)
How does a rocket work?
Rocket fuel is burned, which produces hot gases that expand rapidly and escape out of the back of the rocket. These escaping gases propel the rocket upward.
What is the action force?
The escaping gases
What is the reaction force?
The rocket moving up

15. momentum What does momentum typically mean? Momentum = mass x velocity
Something that is on the move or hard to stop
Momentum = mass x velocity
Momentum is usually abbreviated as “p” and units are kg*m/s

16. momentum
How much momentum does a 0.1 kg baseball have if it is moving at 40m/s?
Momentum = M x V = 0.1kg x 40m/s = 4 kgm/s
How much momentum does a 1200 kg car have if it is also moving at 40 m/s?
Momentum = M x V = 1200 kg x 40m/s = 4800kgm/s

17. momentum The more momentum something has, the harder it is to stop
More mass, more momentum
Does an object at rest have momentum?
No—momentum is not the same as inertia
More velocity, more momentum
How do you increase velocity?
Apply a greater force

19. Momentum
How could an object with a larger mass have the same momentum as an object with a small mass?
If the small object is going much faster
If a 18-wheeler and bicycle are going at the same speed, which has more momentum?
18 wheeler because it has more mass
What happens to a car’s velocity as it slows down?
Velocity decreases
What happens to its momentum?
Also decreases

20. momentum
If you are driving a bumper car and run into another bumper car, what happens to your momentum?
Your momentum transfers to the other car when you hit it

21. Conservation of momentum
Law of Conservation of Momentum: the total momentum of objects that interact does not change (momentum of system before = momentum of system after)
The total momentum of any group of objects remains the same (unless outside forces like gravity or friction act on them)
If the total momentum of 2 cars is 500 kgm/s before a collision, what is the total momentum of them after they collide?
Still 500 kgm/s

24. Work Input = Work Output
Work = Force x distance
Work input is the force that you apply (effort force) x the distance that you apply it through
Work output is the force put out by the machine x the distance moved

25. Mechanical Advantage Machines DO NOT reduce amount of work!
work input = work output!
Remember W = Fxd
If reduce force, must increase distance (*usually what we want!) W=Fd
Or, can reduce distance and increase force W=Fd

27. Machines Provide a mechanical advantage 6 types of simple machines
Increase the magnitude or change the direction of the effort force by increasing effort distance
6 types of simple machines
Inclined plane, wedge, screw, lever, pulley, and wheel & axle

28. Inclined Plane AKA a ramp
Long gradual slope has more mechanical advantage than a steep, short slope

30. Wedge 2 inclined planes back to back MA depends on slope & width
Often used for cutting/splitting
Which amplifies your effort force more, a short thick wedge or a long thin wedge?

32. Screw An inclined plane wrapped around a cylinder
Steeper slope, higher MA

34. Lever
Fulcrum =
Point of rotation

36. Wheel & Axle Several levers radiating out from an axis
MA depends on size

37. A belt or rope around a wheel that can move around its axle
Pulley
A belt or rope around a wheel that can move around its axle
Why do these pulleys have different effort forces? What is the drawback of using the one on the right?

39. Which would you rather use and why?

41. Compound Machines Combination of 2 or more simple machines
Greater mechanical advantage!

43. Machine Efficiency
How can you make a simple machine work more efficiently?
Reduce friction
How?
Make smoother, add lubricant, ball bearings, etc.
How do you know how efficient a machine is?
More of the work you put in is used; less energy is “wasted” as heat (or sound)