Transcript Friction, Gravity, and Elastic Forces Section 10.2 Page 380

Friction, Gravity, and
Elastic Forces
Section 10.2
Page 380
Objectives for 10.2
Identify the two factors that will determine the
friction force between two objects.
Identify the two factors that affect the
gravitational force between two objects.
Be able to draw a force diagram of all forces
acting on an object.
Explain why objects accelerate during free fall.
Explain when matter is considered to be elastic.
Friction
• Friction: The force that one surface exerts
on another when the two rub against each
other.
– Friction acts in the opposite direction of an object’s
movement.
– Friction opposes motion and can eventually cause an
object to stop.
– The strength of friction depends on:
1. The type of surfaces involved
2. How hard the surfaces push together
Sometimes FRICTION can be a
positive thing …
Sometimes FRICTION can be a
negative thing …
• What are some instances when FRICTION
is a positive thing?
• What are some instances when FRICTION
is a negative thing?
Types of Friction
Static Friction
• Friction that acts on objects to prevent them from
moving
Types of Friction
– Sliding Friction
• Friction that occurs when two surfaces slide over
each other
Types of Friction
– Rolling Friction
• Friction that occurs when an object rolls across a
surface
Types of Friction
– Fluid Friction
• Friction that occurs when a solid object moves
through a fluid.
• What is a fluid?
Gravity
• Gravity … a force that pulls objects toward
each other
• Since it acts everywhere, this law is called
the Law of Universal Gravitation:
–Any two objects anywhere
in the universe attract each
other
Gravity
• The force of gravity between objects
depends on:
– The mass of the objects
– The distance between the objects
• The force of gravity between objects
increases with greater mass and
decreases with greater distance
Gravity
Mass vs. Weight
• Mass the amount of matter in an object.
– A jar of nails has more mass than a jar of cotton
balls.
– The SI unit for mass is grams.
• Weight – the amount of gravitational force
exerted on an object
Weight = Mass X Acceleration due to gravity
Gravity and Motion
• Free Fall --- When the force of gravity
alone is acting on an object. (not considering
any wind resistance)
• What will fall fastest …an object of greater
mass or lesser mass?
Gravity and Motion
• Air Resistance --- A type of fluid friction
caused by objects bumping into molecules
in the air.
Gravity and Motion
• Projectile Motion --- Motion from throwing
an object with both a horizontal velocity
and an acceleration vertically due to
gravity
Gravity and Motion
Projectile motion
Projectile
Motion
Elastic Forces
• Matter is considered elastic, IF …
…it returns to its original shape after it is
squeezed or stretched.
Compression
• Compression is an elastic force that
squeezes or pushes matter together
Tension
• Tension is an elastic force that stretches or
pulls matter
Compression and Tension:
Elastic Forces
vid