Forces Notes # 4Static Friction – it pushes back as hard as you push it – no movement – balanced forces

200 Newtons200 Newtons

Sliding Friction• Sliding Friction – the resistance you feel when

pushing something. Usually smaller than the static friction.

• Does a skateboard slow down because nobody is pushing it, or because of friction, or both?

• Does friction always slow things down? Does it ever speed things up?

• Is friction always bad? Explain how hockey players need both low friction and high friction.

Elastic Forces• Elastic Force – the force exerted by a material

when it is stretched or compressed.• Tension Force – a pulling force that makes an

object stretch, and want to pull itself back into its regular shape.

• Compression Force – a squeezing force applied to an object that will make it squish, and want to push back into its regular shape.

Normal Force• Normal Force - The normal force is the support

force exerted upon an object that is in contact with another stable object.– Example: A book on a table is being pushed down by

gravity, but the normal force is the table pushing back.

Sketch the man, the rope, and the cliff – then draw force vectors and label the forces at work.

Which one is the “normal” force?

Sketch two stick figures pulling on the rope. Draw force vectors and label the different forces at work. Be thorough! Don’t leave any force vectors out. Which one is

the “normal” force?

Sketch the “bridge.” Some force vectors are already drawn, but I want you draw more and label them - what kind of forces are at work?

Gravity

Which one is the “normal” force?