Question

how does friction impact everyday life?
friction allows you to hold a pencil and use it to
write on a piece of paper. friction even keeps you from
slipping when you walk.
friction between the tires of a car and the road
allows a car to move. as the wheels of a car turn, they
push against the road. as a result, the road pushes for-
ward on the car. the force pushing the car forward must
be greater than the friction that opposes the motion of
the car. due to friction, a constant force must be applied
to keep the car moving. friction also keeps cars from
moving when parked.

balanced forces (constant speed)
the cars engine produces a
forward force. friction resists
this force. when the forward
force balances the force of
friction, the cars motion does
not change. the car moves at
a constant speed.

unbalanced forces (acceleration)
if the forward force is greater
than the force of friction, the
cars motion changes. the car
accelerates forward.

balanced forces (no motion)
the force of gravity pulls the truck
down the hill. friction between the
trucks wheels and the road resists
the force of gravity. when the force
of friction is equal to the force of
gravity, the trucks motion does not
change. the truck does not move.

increasing and decreasing friction
sometimes, people need to decrease the friction
between surfaces. for example, car engines have many
moving parts. if there is too much friction between these
parts, the engine can become too hot. therefore, people
add oil to their engines. oil is a lubricant. it reduces the
friction between surfaces.
sometimes, people need to increase the friction
between surfaces. for example, people in cold climates
may put sand on icy roads and sidewalks. the sand
increases friction between the ground and people or cars
moving on it.

talk about it
discuss with a partner or in
a small group, identify 10
different examples of how
friction affects your everyday
life. for each example, talk
about whether friction makes
things easier or more difficult.

looking closer

1. apply concepts what

would happen to the truck
in the bottom picture if the
force of gravity were larger
than the force of friction?

reading check

1. define what is a

lubricant?

copyright © by holt, rinehart and winston. all rights reserved.
interactive reader
247
motion

Explanation:

A lubricant is a substance that reduces friction between surfaces. In the text, oil is given as an example of a lubricant used in car engines to reduce friction between moving parts.

Answer:

A lubricant is a substance that reduces friction between surfaces.