10-2: Friction, Gravity, & Elastic Forces

What factors determine the strength of the friction force between two surfaces?

Anticipatory Set

Why can he move an elephant with only his finger?

California StandardsScience Standard 8.2.b: Students know when

an object is subject to two or more forces at once, the result is the cumulative effect of all the forces.

Science Standard 8.2.d: Students know how to identify separately the two or more forces that are acting on a single static object, including gravity, elastic forces due to tension or compression in matter and friction.

Inputfriction: a force that two surfaces exert on

each other when they rub against each other.static friction: the friction that acts on

objects that are not moving.sliding friction: two solid surfaces slide over

each other.rolling friction: an object rolls across a

surface.

Inputfluid friction: a solid object moves through a

fluid.gravity: a force that pulls objects toward

each other.mass: the measure of the amount of matter

in an objectweight: the gravitational force exerted on a

person or object at the surface of a planet.

Inputfree fall: the only force acting on an object is

gravity.air resistance: an upward force exerted on

falling objects.projectile: an object that is thrown.compression: an elastic force that squeezes

or pushes matter together.tension: an elastic force that stretches or

pulls matter.

Input & ModelingFriction

The strength of the force of friction depends on the types of surfaces involved and on how hard the surfaces push together.There are four types of friction…

Input & ModelingStatic Friction

Input & ModelingSliding Friction

Once the box is moving,

there is sliding friction

between the box and the

floor.

Input & ModelingRolling Friction

Input & ModelingFluid Friction

Input & ModelingGravity

The force of gravity between objects increases with greater mass and decreases with greater distance.

Weight = Mass x Acceleration due to gravity

Input & ModelingGravity

Gravity Between Objects

Input & ModelingGravity and Motion

In free fall, the force of gravity alone causes an object to accelerate in the downward direction.

free fallair resistanceprojectile motion

Input & Modeling

Free Fall

Projectile Motion

Air Resistance

Input & ModelingElastic Forces

Matter is considered elastic if it returns to its original shape after it is squeezed or stretched.

CompressionTension

HOMEWORK CONNECTION Read pages 380-388 in your Science textbook.

Complete the Section 10-2 Review & Reinforce

Write a detailed SUMMARY of the section and complete the UNANSWERED QUESTIONS section of your notes.

Choose two of the remaining Depth & Complexity ICONS in your notes and explain how they relate to this section.