1. Force, Friction, Gravity, &
Elastic Forces

2. Forces 1
 What is force?
 What is an example of force?

3. Forces 2
 Force is simply defined as a push or a
pull.
 Force is described by it’s magnitude
(strength) and by the direction in which it
acts.
 The SI unit of measure for the
magnitude of a force is Newton (N)

4. Forces 3
 The combination of all forces acting on
an object is referred to as the net force.
 ALWAYS SHOW THE DIRECTION OF
ALL FORCES!!!!!!

5. Forces 4
 When two forces are acting in the same
direction, they produce a larger net
force. (add, both #s are positive)
 When two forces are acting in opposite
directions, they produce a net force in
the direction of the larger force.
 Equal opposite forces cancel out and
produce no net force. (no movement)

6. Friction 1
 Friction is a force that two surfaces exert
on each other when they rub against
each other.
 If there weren’t friction (like in space)
objects would just keep moving until
they ran into something.

7. Friction 2
 Strength of friction depends on two
things:
Types of surfaces involved
How hard the surfaces push
together

8. Friction 3
 Static Friction is the friction that acts on
an object that is not in motion.
Examples?
 Sliding Friction is friction that acts
when two solid surfaces slide over each
other. Examples?

9. Friction 4
 Rolling Friction is the friction acting
when an object is rolling. Rolling friction
is less than sliding friction. Examples?
 Fluid Friction is the friction that occurs
when a solid object moves through a
fluid and is less than sliding friction.
Examples?

10. Gravity 1
 What is gravity?
 Gravity is a force that pulls objects
toward each other.
 Gravity acts everywhere in the universe-
not just Earth!

11. Gravity 2
 The force of gravity increases between
objects with greater mass and
decreases with greater distance.
 Make sense? Examples?

12. Gravity 3
 Gravity and Weight- remember:
Weight is a reflection of the gravitational pull
on an object.
Formula for calculating weight is…
Weight = Mass x Acceleration from Gravity

13. Gravity 4
 Gravity and motion! What goes up, must
come down.
 Free Fall is when the force of only
gravity is causing an object to accelerate
in a downward direction.
These objects will accelerate at 9.8m/s2
(This means that the speed will increase by
9.8 m/s every second. WOW!)

14. Gravity 5
 Air Resistance is an upward force that
acts on objects as they fall through the
air.
The larger the surface area, the more air
resistance, the slower the object falls.
Example: Leaf vs. a ball

15. Gravity 6
 Projectile Motion is the motion an
object experiences when it’s been
thrown.
Objects thrown horizontally will land at the
same time as an object dropped if released
at the same time. (Gravity acts on both of
them).

16. Elastic Forces 1
 Something is considered to be elastic if
it returns to it’s original shape after it’s
squeezed or stretched.
Compression is the elastic force that
squeezes or pushes matter together.
Tension is the elastic force that stretches or
pulls matter apart.