Page 14 - Science Course 2 (Book 2)

Mo8-L1b: How Does Gravity Affect Forces?

An object’s weight is proportional to its mass. Up to a limit, the strength of static friction changes
to match the applied force.
Near Earth’s surface, the weight of an object in
newtons is about ten times its mass in kilograms. Sliding friction opposes the motion of surfaces slid-
ing past each other.

120kg

Friction

Friction is a force that opposes the movement
between two touching surfaces.

There are several types of friction. For example: Fluid friction is friction between a surface and a
• Static friction f uid—any material, such as water or air, that f ows.
• Sliding friction
• Fluid friction Fluid friction between a surface and air is air
resistance.

What causes friction between surfaces?

When the microscopic dips and bumps on one
Static friction prevents surfaces from sliding past surface catch the dips and bumps on another
each other. surface, the microscopic roughness slows sliding.

This is a source of friction.

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