1. Chapter 10 force and motion STUDY GUIDE/NOTES
FRICTION
GRAVITY
NEWTON’S LAWS OF MOTION

2. What is Friction?
The force that 2 surfaces exert on each other when they rub against each other.
Types of Friction
Static friction
Sliding friction
Rolling friction
Fluid friction

3. What are the Causes of Friction?
The strength of the force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved.
Smooth surfaces have less friction; bumpy surfaces have more
Friction acts in a direction opposite to the direction of the object’s motion

4. What is Static Friction?
Friction that acts on objects that are not moving
Because of static friction, you must use more force to start the motion of stationary objects
Once you start an object moving there is no longer static friction

5. What is Sliding Friction
Occurs when 2 solid surfaces slide over each other
Examples: spreading sand on icy path
Ballet dancers applying resin to ballet slippers so they don’t slip
Bicycle brakes
Skinning your knee

6. What is Rolling Friction
Occurs when an object rolls across a surface
Easier to overcome than sliding friction for similar materials
Ball bearings are in moving objects such as skates, skateboards, and bicycles
Ball bearings reduce friction by rolling between moving parts

7. What is Fluid Friction
Occurs when solid objects move through a fluid like a gas(air) or liquid
Easier to overcome than sliding friction
Reason why moving parts are often bathed in oil or other lubricants
Fluid friction occurs between a bicyclist and the air. Bicyclists often wear streamlined helmets and clothes

8. How can we reduce the friction between 2 objects?
Reduce the contact area by using rollers/ball-bearings/wheels
Change the surfaces of the materials that are touching by using lubrication ex. Oil
Create a cushion of air
EXAMPLE. Like a hovercraft or air hockey table

9. Low friction
Ski’s on the snow WATER ON A SLIDE

10. High friction
Brakes on a bike PENCIL AND ERASER CAR TIRE

11. FACTORS THAT AFFECT FRICTION
SURFACE AREA- HOW MUCH CONTACT BETWEEN THE 2 SURFACES RUBBING TOGETHER- MORE CONTACT WITH SURFACE , MORE FRICTION
TEXTURE- ROUGHER SURFACES CREATE MORE FRICTION THAN SMOOTHER SURFACES
MASS/WEIGHT- LARGER OBJECTS CREATE MORE FRICTION THAN SMALLER ONES. LARGER OJBECTS ARE HARDER TO MOVE.

12. What is a force?
A force is a push or pull that causes an object to move, stop, or change direction
In physics a force is anything that makes an object accelerate

14. Force Forces come in pairs Forces have a magnitude and a direction
Magnitude: 5N
Direction: north (up)
5N, north (up)

15. Balanced and Unbalanced Forces
Forces occur in pairs and they can be either balanced or unbalanced

16. Balanced Forces Balanced forces do not cause change in motion
They are equal in size and opposite in direction

17. Some Examples from Real Life
A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion.
Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.

18. Unbalanced Forces An unbalanced force always causes a change in motion
When unbalanced forces act in opposite directions you can find the net force
Net force
Magnitude
The difference between the two forces
Direction
Direction of the largest force

19. Unbalanced Forces
3 N, right – 6 N, left = 3N, left

20. Unbalanced Forces
4 N, left – 10 N, right =
6N, right

21. Unbalanced Forces
5 N, right + 10 N, right =
15N, right