static and Kinetic Friction
If you try to slide a heavy box resting on the floor, you may find it difficult to get the box
moving. Static friction is the force that is counters your force on the box. If you apply a lig
...
static and Kinetic Friction
If you try to slide a heavy box resting on the floor, you may find it difficult to get the box
moving. Static friction is the force that is counters your force on the box. If you apply a light
horizontal push that does not move the box, the static friction force is also small and directly
opposite to your push. If you push harder, the friction force increases to match the magnitude of
your push. There is a limit to the magnitude of static friction, so eventually, you may be able to
apply a force larger than the maximum static force, and the box will move. The maximum static
friction force is sometimes referred to as starting friction. We model static friction, Fstatic, with
the inequality Fstatic s N where s is the coefficient of static friction and N the normal force
exerted by a surface on the object. The normal force is defined as the perpendicular component
of the force exerted by the surface. In this case, the normal force is equal to the weight of the
object.
Once the box starts to slide, you must continue to exert a force to keep the object moving, or
friction will slow it to a stop. The friction acting on the box while it is moving is called kinetic
friction. In order to slide the box with a constant velocity, a force equivalent to the force of
kinetic friction must be applied. Kinetic friction is sometimes referred to as sliding friction. Both
static and kinetic friction depend on the surfaces of the box and the floor, and on how hard the
box and floor are pressed together. We model kinetic friction with Fkinetic = k N, where k is the
coefficient of kinetic friction.
In this experiment, you will use a Force Sensor to study static friction and kinetic friction on a
wooden block.
OBJECTIVES
• Use a Dual-Range Force Sensor to measure the force of static friction.
• Determine the relationship between force of static friction and the weight of an object.
• Measure the coefficients of static and kinetic friction for a particular block and track.
• Determine if the coefficient of kinetic friction depends on weight.
MATERIALS
computer string
Vernier computer interface block of wood with hook
Logger Pro balance or scale
Vernier Force Sensor mass set
SIMULATION ADDRESS
12 - 2 Physics with Vernier
PRELIMINARY QUESTIONS
1. In pushing a heavy box across the floor, is the force you need to apply to start the box moving
greater than, less than, or the same as the force needed to keep the box moving? On what are
you basing your choice?
2. How do you think the force of friction is related to the weight of the box? Explain.
PROCEDURE
Part I Starting Friction
1. Before clicking begin, read the description of the activity. Once the object begins moving,
what do we know about its velocity?
2. Once you click begin, the simulation shows a block connected by a string to a force
sensor. The screen of the sensor’s interface is shown in the box on the top right. The type
of object and the surface it rests on can be chosen in the top left
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