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10-2: Friction, Gravity, & Elastic Forces
What factors determine the strength of the friction force between two surfaces?

Why can he move an elephant with only his finger?
Anticipatory Set Why can he move an elephant with only his finger?

California Standards Science 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.

Input friction: 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.

Input fluid 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 object weight: the gravitational force exerted on a person or object at the surface of a planet.

Input free 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 & Modeling Friction
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 & Modeling Static Friction

Input & Modeling Sliding Friction
Once the box is moving, there is sliding friction between the box and the floor.

Input & Modeling Rolling Friction

Input & Modeling Fluid Friction

Input & Modeling Gravity
The force of gravity between objects increases with greater mass and decreases with greater distance. Weight = Mass x Acceleration due to gravity

Gravity Between Objects
Input & Modeling Gravity Gravity Between Objects

Input & Modeling Gravity and Motion
In free fall, the force of gravity alone causes an object to accelerate in the downward direction. free fall air resistance projectile motion

Input & Modeling Projectile Motion Free Fall Air Resistance

Input & Modeling Elastic Forces
Matter is considered elastic if it returns to its original shape after it is squeezed or stretched. Compression Tension

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.

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