Page 251 - Science Course 3 (Book 1)

Mo7-L2b: What is Friction?

Friction and the Law of Conservation of Energy
Mo7-L2b What is Friction?
What happens to mechanical energy when you apply
the bicycle brakes and the bicycle stops?
KEY CONCEPTS:
1. What happens to energy when it is used?
A moving bicycle has
mechanical energy.
When you apply the
Vocabulary A-Z brakes, the bicycle’s
mechanical energy is
Let us learn some vocabulary not destroyed.

Friction

a contact force that resists the sliding motion of two
surfaces that are touching
The mechanical energy is transformed into thermal
energy. Friction between the brake pad and the
moving wheel transforms mechanical energy into
thermal energy.

Pushing Force
Motion
Friction

Let’s Begin There is always friction between any two surfaces
that are rubbing against each other.

Using Energy
The Law of Conservation of Energy When you use energy, you usually change it from

Friction is a force that resists the sliding of two one form into another.
surfaces that are touching.
All forms of energy can be transformed into
thermal energy.
Motion
During photosynthesis, a plant transforms the
Sun’s radiant energy into chemical energy that it
stores in chemical compounds.
Pushing Force

Motion
Friction
Friction is a force that acts in an opposite direction
to movement.

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