Friction is the force of one surface rubbing or gripping on another.

Rough surfaces are uneven or irregular, they are not smooth.

An irregularity is something different to what is expected.

If something is microscopic, it is so small you need a microscope to be able to see it.

A lubricant is a substance added between two surfaces to reduce friction.

Friction

Science

In the Hidden forces unit, they will build on this knowledge to learn about turning forces, forces that hold objects on a surface, and those that make some objects float.

In primary science, pupils learnt that air resistance, water resistance and friction push back against moving objects. 

Forces

The force of one surface touching another surface.

The force of one surface repelling another surface.

The force of one surface gripping or rubbing on another surface.

Which best describes what a friction force is?

Which picture shows the friction force of the ice on the sliding puck?

The size of a friction force between dry surfaces is affected by how {{}} the surfaces are. 

Any substance added between two surfaces to reduce friction is called a ...

Lubricants should stay in place and not promote rusting.

Lubricants keep surfaces slightly further apart.

Which gives the best explanation of how lubricants reduce friction?

The size of the friction force between two surfaces can change.

Friction forces only act when there is movement.

Friction occurs when tiny irregularities catch, producing backwards forces.

The force from the air that slows down moving objects.

Which is the best description of a friction force?

Which factor can affect the size of the friction force acting when an object slides over a surface?

Give the correct direction: Friction forces always act {{}} on a moving object. 

Friction forces slow down moving objects.

Friction forces pull objects back down towards planet Earth.

Which sentences describe the correct effects that friction forces can have on objects?

If a slippery liquid or grease was added between the object and the surface.

An object is sliding along a surface. Which of the following can reduce the friction force?

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