Slide 3

Friction & Traction

Friction

Look at the following picture: There are two tractors, and each has a push a load of bricks across the floor. Each pile of bricks has the same surface area in contact with the floor (i.e. the same dimensions of bricks making up the bottom level) however their masses vary drastically.

Which will require more force to move?

It is quite intuitive that the 400-pound load of bricks will require more force to move it than the 100-pound load. This is because there is more friction due to mass between the load and the floor with the 400-pound pile compared to the 100-pound pile.

Although the bricks appear smooth, there are quite rough on a microscopic level. It is the interaction between the surface of the bricks and the surface of the floor that makes up friction.

(Nice 2012)

Now imagine the same situation, but instead of a warehouse floor, the bricks are resting on slipper ice. Is more or less force required to move them?

The answer is less, because the coefficient of friction, or how much force is needed to slide across a surface, is lower on slippery ice than concrete.

Traction

Try this at home!

Take a spring scale (the kind that measures an object’s mass by hanging it from the scale) and attach it to a somewhat heavy object like the picture below.

Spring Scale Traction Test

                (Giancoli 2005 pg 73)

        Now slowly pull the scale parallel to the surface until you reach the maximum value on the scale. You will notice that the maximum value occurs immediately before the object begins to slide along the surface; when the object is in motion, there is less force required to keep it moving than initially moving it when it is standing still.
        This is what is known as traction, or how much force is required before an object slips. Traction has a direct relationship with friction, so surfaces with high friction also have high traction. What is important to remember is that a stationary object has traction, and the most amount of force an object needs to be in motion is at rest.

Winter Driving Scenario
Friction & Traction

Applying the Brakes

Bibliography

	Friction & Traction Friction Look at the following picture: There are two tractors, and each has a push a load of bricks across the floor. Each pile of bricks has the same surface area in contact with the floor (i.e. the same dimensions of bricks making up the bottom level) however their masses vary drastically. Which will require more force to move? It is quite intuitive that the 400-pound load of bricks will require more force to move it than the 100-pound load. This is because there is more friction due to mass between the load and the floor with the 400-pound pile compared to the 100-pound pile. Although the bricks appear smooth, there are quite rough on a microscopic level. It is the interaction between the surface of the bricks and the surface of the floor that makes up friction. (Nice 2012) Now imagine the same situation, but instead of a warehouse floor, the bricks are resting on slipper ice. Is more or less force required to move them? The answer is less, because the coefficient of friction, or how much force is needed to slide across a surface, is lower on slippery ice than concrete. Traction Try this at home! Take a spring scale (the kind that measures an object’s mass by hanging it from the scale) and attach it to a somewhat heavy object like the picture below. (Giancoli 2005 pg 73) Now slowly pull the scale parallel to the surface until you reach the maximum value on the scale. You will notice that the maximum value occurs immediately before the object begins to slide along the surface; when the object is in motion, there is less force required to keep it moving than initially moving it when it is standing still. This is what is known as traction, or how much force is required before an object slips. Traction has a direct relationship with friction, so surfaces with high friction also have high traction. What is important to remember is that a stationary object has traction, and the most amount of force an object needs to be in motion is at rest.
	Winter Driving Scenario Friction & Traction Applying the Brakes Bibliography