F=MA

Why does the box stop?

Box

Surface

Friction is the force resisting

the motion of objects sliding

against each other.

Friction is a force!

F=MA ForceFrictionForce

Friction always apposes motion

Three types of frictionStatic Friction

Static means “no motion”Static friction is the friction force that prevents two surfaces at rest from sliding past each other.

Apply Force

As you apply force, friction force increases

Friction Force

When applied force is greater than friction force, the object begins to move

Three types of frictionSliding Friction

Sliding friction is the friction force that opposes the motion of an object along a surface.

Static friction is before an object movesSliding friction is when the object is in motion

Three types of frictionRolling Friction

Rolling friction is the friction force that opposes the motion of a circluar object along a surface.

Three types of friction

Static Friction > Sliding Friction > Rolling Friction

All friction opposes motion

Equation

𝐹 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛=𝜇∗𝑀∗𝑔

Newton’s First Law

• Also called: Newton’s Law of Inertia

• Inertia is the resistance to motion due to mass

More Mass = More Inertia

Example

Elephant has more inertia ‘than a human

Which means, it’s harder to change an elephant’s motion than

a human’s motion.

More inertia, means more force to get it moving

50 kg Force

100 kg 2 x Force

150 kg 3 x Force

More Mass = More Inertia

More Inertia = More Resistance

Friction Force• Depends on surface and shape of object

Inertia• Depends on mass of the object