1. Motion and Forces

2. Force Force: a push or pull on an object
Force causes the motion of an object to move in the direction of the force

3. Force Force does not always change an objects velocity
Net Force: combining 2 or more forces are acting on an object

5. Balanced Forces
Balanced Forces: when the net forces on an object are equal and in opposite directions

6. Unbalanced Forces
Unbalanced Forces: forces in opposite directions that are not equal
Box will move in the direction of the stronger force

7. Inertia
Inertia: the tendency of an object to resist any change in its motion
The greater the mass of the object the greater its inertia is

8. Newton’s 1st Law of Motion
Newton’s 1st Law of Motion: an object at rest tends to stay at rest and an object in motion tends to stay in motion until acted upon by an outside force

9. Car Crashes
Example: if a car traveling at 50 km/h (31 mph) hit a solid object head on, the car crumples, slows down and stops in 0.1 seconds!
Any passenger not wearing a seatbelt will continue to travel at the same speed the car was traveling

10. Car Crash
The passengers are traveling at 50 km/h, which is the same speed they would reach falling out of a 3 story building!

11. Safety Belts
The force exerted on a person in this type of crash is equal to 14 times the force of gravity
The safety belt is attached to the car, therefore it slows down at the same speed as the car does so it helps to slow the person as well

12. Force, Mass and Acceleration
Think about force, mass and acceleration:
What is the difference between throwing a ball as hard as you can and tossing it gently?
Which ball would have a greater acceleration? And why?

13. Force, Mass and Acceleration
If you throw a baseball and a softball as hard as you can, do they have the same speed?
Why?
Mass of baseball = 0.20 kg
Mass of softball = 0.14 kg
Even though you exerted the same FORCE, the baseball will have a different velocity due to its mass!
MASS, FORCE AND ACCELERATION ARE RELATED!

14. Bowling ball or tennis ball?
Which object has greater inertia?
Which object will have greater velocity if thrown?
Which will have a greater acceleration?

15. Newton’s 2nd Law of Motion
Newton’s 2nd Law of Motion: the acceleration of an object is in the same direction as the net force on that object
Depends on 2 things:
The net force acting on the object
The objects mass

16. Acceleration Equation
a = net force (in Newtons)
Mass (in kg)
You push a friend on a sled, your friend and the sled together have a mass of 70 kg. If the net force on the sled is 35 N, what is the sleds acceleration?

17. Acceleration Example a = 35 N = 0.5 N/kg or m/s² 70 kg
If the mass of a helicopter is 4500 kg, and the net force on it is N, what is its acceleration?
What is the net force on a race car with a mass of 900 kg if its acceleration is 32 m/s²?
A car is being pulled by a tow truck, what is the car’s mass if the net force on it is N and it has an acceleration of 2 m/s²?

18. Friction
Friction: the force that opposes the sliding motion of 2 surfaces
Depends on 2 factors:
The type of surfaces
The force pressing the surfaces together

19. Static Friction
Static Friction: the frictional force that prevents 2 surfaces from sliding past each other
This is why it is hard to get something to move in the first place

20. Sliding Friction
Sliding Friction: the force that opposes the motion of 2 surfaces sliding past each other
This is why when you are sliding something along the floor, it quickly comes to a stop when you stop pushing on it

21. Rolling Friction
As a wheel rolls over a surface the wheel “digs in” to the surface causing the wheel to move over the surface
When there is not enough rolling friction the tire will just spin
Example: a car stuck in the snow

22. Air Resistance
Air Resistance: opposes the motion of objects that move through the air
Causes objects to fall at different speeds

23. Terminal Velocity
As an object falls its velocity increases, but so does air resistance
Terminal Velocity: when the upward force is equal to the downward force on a falling object

24. Terminal Velocity The net force = zero
The object is falling at a constant velocity and NOT accelerating anymore
The terminal velocity of an object depends on:
Size
Shape
Mass
Example: a parachute has more air resistance than a falling skydiver with a closed parachute