1. Forces and Friction

2. THINK!
In the clip, what causes the tractor to start moving?

3. FORCE: action exerted on a body in order to change the body’s state of ___________________________.
A __________________ or a ___________________
Cause acceleration or deceleration! (You can’t change your motion without a force)
Force is a __________________________ (has magnitude and direction).
Units are __________________________

4. NET FORCE: the ___________________ ___________________ ___________________ ___________________ acting on an object.
If net force is zero, object will ________ accelerate (it stay at rest or constant velocity).
Force of the bat’s legs holding it up
Force of gravity pulling down

5. BALANCED FORCES: More than one force acting on an object that
has a net force equal to ________
Forces are equal in _____________ and opposite in _________________________
Objects affected by balanced forces either:
Do NOT MOVE or
Move at CONSTANT VELOCITY
(__________________________
__________________________)
100 N east
100 N west
Net force = ___
100 N west
100 N east
Net force = ___

6. UNBALANCED FORCES: More than one force acting on an
object that has a net force UNEQUAL to _____________
Have a net force that does NOT ______________________
Must be present to cause any change in an object’s state of __________________ or __________________.
Causes the ____________________________ to change (acceleration or deceleration)
west
east
Net force = ________

7. THINK! Balanced or unbalanced? A parked car:
A car at a constant speed:
A car accelerating:

8. Balanced or Unbalanced?
Net Force =
100 N right
100 N left
Will the truck accelerate?
Balanced or Unbalanced?
Net Force =
100 N right
60 N left
Will the truck accelerate?
Balanced or Unbalanced?
Net Force =
south
Will the plane accelerate?
north

9. FRICTION

10. THINK! How do you know friction is at work in this clip?

11. Occurs between ________ surfaces
FRICTION: Force that opposes _______________________ between two surfaces that are in contact.
Occurs between ________ surfaces
Molecular Adhesion
Surface roughness
___________________ the applied force.
Converts kinetic energy to _________________________
For motion to change, the force applied to an object must be ____________________________friction
100 N west
Net force = _______
100 N east

12. Net Force ________
Net Force _______
Net Force _______

13. TYPES OF FRICTION
STATIC FRICTION: resists the initiation of motion between two surfaces that are in contact and ___________________.
Static friction is ____________________________kinetic friction.
KINETIC FRICTION: opposes the movement of two surfaces that are in contact and are ______________________.
There are 3 types of kinetic friction you need to know:
SLIDING FRICTION: Two objects _______________________ each other
ROLLING FRICTION: Round object rolling over a flat surface
FLUID FRICTION: Force that resists the movement of a solid
object through a fluid (________________________________).

14. Static Friction Kinetic Friction
The point where the object starts moving and the friction goes from static to kinetic
Kinetic Friction

15. THINK!
What are the 2 types of friction?
How are they different?

16. Sliding Friction
Rolling Friction
Fluid Friction

17. Drag is fluid friction that affects cars, airplanes, boats, etc.

18. THINK!
In each clip what type of friction do you see? How do you know?
Clip 1:
Clip 2:
Clip 3:

19. Friction can be _______________________
Necessary to walk, hold an object, strike a match, etc.
Important for braking
Causes excessive heating or wear of moving parts
Decreases fuel efficiency

20. WAYS TO REDUCE HARMFUL FRICTION
Replace sliding friction with __________ friction
Use _________________
Use ______________________________
Make surfaces ________________

21. WAYS TO INCREASE HELPFUL FRICTION
Make surfaces _______________________
Add __________________________________
Increase _______________ on two objects
(Example: adding ______________________ _____________________________________)

22. THINK! What is one way that friction can be good?
What is one way that friction can be bad?