1. 10.2 Friction, Gravity, and Elastic Forces
Mr. Sapalicio
Physical Science
Monterey Highlands Elementary

2. Friction
Friction- is a force that 2 surfaces exert on each other when they rub against each other.
Without friction moving objects would not stop moving until it strikes another object.

3. Causes of Friction
Smooth surfaces produce less friction than rough surfaces.
*The strength of the force of friction depends on the types of surfaces involved and on how hard the surfaces push together.*

4. Static Friction
Static friction- friction that acts on objects that are NOT moving.
This friction can be observed when you try to move a desk
Static friction is a beginning amount of friction or force you must overcome to move an object that is not moving.
Static friction acts in the opposite direction of intended motion.
Static character?- a character that does not change throughout the story.
Relate to science- an object that does not move and will not until you put more than the static force required to move it.

5. Static Friction
In order to pull this truck the man had to exert more force than the static friction.
Static friction works in the opposite direction of the intended motion.

6. Sliding Friction
Sliding friction- occurs when 2 solid surfaces slide over each other.

7. Example of Sliding Friction

8. Rolling Friction
Rolling friction- when an object rolls across a surface.
Rolling friction is less than sliding friction (meaning it does not hold back as strongly as a sliding)
Sliding friction
Rolling friction

9. Fluid Friction
Fluid Friction- when a solid object moves through a fluid.
fluids such as oils, water, AIR.
Fluid friction is less than rolling and sliding.
Which is which?

10. Friction Friction is greater... between rough surfaces
when there’s a greater force between the surfaces (e.g. more weight)

11. What are 2 ways that friction can be useful?
Friction question?????????????????????
What are 2 ways that friction can be useful?

12. What type of friction is this?

13. Gravity Gravity- a force that pulls the object towards each other.
Gravity acts everywhere in the universe not just Earth.
Any 2 objects in the universe attract each other.

14. Gravity- Mass and Distance
*The force of gravity between objects increases with greater mass and decreases with greater distance. *
Mass- the measure of the amount of matter in an object.
The more mass an object has the more gravitational force.
The further away 2 objects are the less gravitational force.

15. Gravity
Who experiences more gravity - the astronaut or the politician?
Which exerts more gravity -
the Earth or the moon?
more mass
less distance

16. Gravity and Weight
Weight- the gravitational force exerted on a person or object at the surface of a planet.
Formula for weight:
Weight= MASS X Acceleration due to gravity.
W:(Newtons) depends on gravity
M: (Kg) always the same
g: (acceleration due to gravity (m/s2))
Earth’s acceleration will always be 9.8m/s2.
So if you weighed 50kg you would multiply that by the acceleration of gravity on Earth 9.8m/s2 = 490N.

17. Gravity Would you weigh more on Earth or Jupiter? Jupiter because...
greater mass
greater gravity
greater weight

18. Gravity and Motion
Free fall- when the only force acting on an object is gravity.
*In free fall, the force of gravity alone causes an object to accelerate in the downward direction. *

19. Animation from “Multimedia Physics Studios.”
Gravity and Motion
Acceleration. due to gravity (g)
In the absence of air resistance, all falling objects have the same acceleration!
On Earth: g = 9.8 m/s2
elephant
feather
Animation from “Multimedia Physics Studios.”

20. Elastic Forces
Compression force- an elastic force that squeezes or pushes matter together.
Example: dog on the couch, exerts compression force onto the cushion. Cushion pushes back with equal force in opposite direction.
Forces are balanced that’s why you don’t sink into couch.
*Matter is considered elastic if it returns to its original shape after it is squeezed or stretched. *
Compression- what happens to the object.

21. Elastic Forces
Tension- the elastic force that stretches or pulls matter. The force of pull supplied by strings, ropes or chains is called the tension force Tension is the force of pulling.

22. Work on
Math Practice page 386 # 1-4