Download 9/29 Friction HW

Name: _______________________________
Friction
Friction force is the force caused by a surface as an object moves across it or makes an effort to move
across it. For example, when we were sliding the book across the table in several of our experiments, it
took a little bit of force to make the book move. This little bit of force is because of friction.
Sliding Friction
There are two types of friction force. The first type happens when something is in motion and in contact
with a surface. Whether skidding across the sidewalk like when you grab your breaks to skid your bike
tires or driving a car, any time there is movement across a surface happening, we refer to this as sliding
friction.
Sliding friction occurs when something slides across a surface (like our book sliding across the table). The
table offers resistance to the movement of the book. We often say that the table exerts
a friction force on the book. This is an example of a sliding friction force because it
results from the sliding motion of the book.
If a car slams on its brakes and skids to a stop like the sign to the right, there is a sliding
friction force exerted on the car tires by the roadway surface. This friction force is also a
sliding friction force because the car is sliding across the road surface.
Static Friction
Friction forces can also exist when something is not moving but we are trying to move it. That’s a big
“but” because it describes the one major difference between these two types of friction. Which is…
For an example, I have a mental image of someone trying to pull a box
but the box won’t move across the floor (like the guy to the right).
The force preventing the box from moving is called static friction.
Static friction occurs when two surfaces are not moving relative to
each other but something or someone must be applying a force to it.
A force must exists on the objects (the guy pulling) to try to get it to
move. If there’s no force, then there’s no static friction. Once the box starts to move, then we have
overcome the static friction.
1. Sliding friction has to be in ______________________ and ________________________.
2. Static friction has to be _________________________________
3. So the one major difference between sliding and static friction is…
___________________________________________________________________________________
4. Based on the two types of friction, the bottom line is that friction does what…
5. The groceries on this table are a bad example of static friction because…