Friction is an invisible __________________.

Friction is an invisible force that occurs when objects come into ___________ with each other.

_________ is a force that acts against or resists movement so that things slow down or even stop moving.

Friction is a _________ that acts against or resists movement so that things slow down or even stop moving.

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Studying friction is important because you can understand how wheels work. This is good when you drive a car or ride a bicycle.

The pushing force = friction, so the box does not move.

The pushing force < friction, so the box moves across the floor.