1. Newton’s Second Law of Motion
Ch. 4

2. What is Acceleration?
A change in velocity over time

3. What Produces Acceleration?
Force
A hockey puck at rest on ice moves once you apply a force and begins to accelerate.
When the stick isn’t pushing it, the puck stays at a constant velocity
APPLIED FORCE PRODUCES ACCELERATION

4. Acceleration Depends on the Net Force
This makes sense right? The object will move in compliance to what forces are acting on it.
So if you double the net force, the acceleration doubles

5. Acceleration ~ Net Force
An object’s acceleration is directly proportional to the net force acting on it
“~” Stands for directly proportional to
Meaning that if one doubles the other doubles

6. Friction
When you apply a force to an object, friction usually reduces the net force and thus, the acceleration
Atoms cling together at many points of contact when slid against each other creating friction

7. Friction
The direction of the friction force is always in a direction opposing motion

9. Friction

10. Friction
To push a heavy box, you must apply enough force to overcome friction
So you have to be winning the net force battle

11. Static Friction vs. Sliding Friction
The initial force to get a stationary object to move
If you push on a crate, it takes more force to get it going than it takes to keep it sliding.
The force of friction of a sliding object
The force of friction against the tires of a sliding car

12. The Force of Friction Does not depend on speed!
A car skidding at low speed has the same friction as a car skidding at high speed
If the car that slides at a low speed with a frictional force of 90 N, the high speed car will also have a frictional force of 90 N

13. Fluid Friction Friction in liquids and gases
Occurs as an object pushes aside the fluid it is moving through
Trying to run through water… yeah there is some fluid friction there
FLUID FRICTION DOES DEPEND ON SPEED

14. Air resistance (or any fluid friction) increases with increasing speed
FLUID FRICTION DOES DEPEND ON SPEED
So think of air resistance (or air drag)
If you are jogging you don’t notice air resistance so much
However, if you are in a jet, it is pretty noticeable
Air resistance (or any fluid friction) increases with increasing speed

15. Friction – The Bill Nye Way
Bill Nye - Friction