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Unit 1: Mechanics Page 15

accelerated towards the Earth at 8. Weight is a measure of how
the same rate of speed. much gravity is pulling on an

7. Gravity does pull on things object.
differently. Gravity is pulling 9. Mass is a measure of how much
greater on objects that weigh matter (how many atoms) make
more. up an object.

Lesson 3: Friction

If you answered friction, you’re pressure is put on the
right. But what is friction really? materials. Whether the
Would your hands feel warmer if materials are wet or dry.

they were larger? Or rougher? Or Whether they are hot or
darker? What sorts of things affect cold…in other words, it’s
the amount of friction between two quite complicated!
surfaces? 3. Static friction is the friction

between two objects that are
If you read a textbook from twenty
years ago, you’ll find some things not moving.
have changed about how we think 4. Kinetic friction is the friction
about friction. Engineers used to between two objects where
only look at surface roughness… at least one of them is
but then they took a look on the moving.
molecular level and saw a few 5. Friction happens due to the
things that made us update our electro-magnetic forces

way of thinking about treads. between two objects.

1. Friction is the force between 6. Friction is not necessarily due

two objects in contact with to the roughness of the
one another. objects but rather to
chemical bonds “sticking and
2. Friction is dependent on the slipping” over one another.
materials that are in contact

with one another. How much

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