Name ______________________________
Ms. Sabbatino
Date ___________
Period _________
Lab #7: Which Factors Affect the Friction Force?
Background:
Friction is a force that exists all around us. The question is WHAT does the
friction force actually depend on? We will work as a class to determine which of the
factors listed below actually affect the friction force. Each group will be responsible for
investigating ONE of the factors below. They will come up with their own procedure,
complete the experiment, log data, and come up with a conclusion on whether their factor
affects friction or not. We will be using the ideas of equilibrium to measure the friction
force. We know that friction will act horizontally along the surface opposing motion.
This means, if we keep the object in equilibrium the force we apply horizontally on the
block will be equal to the friction force. We will use a spring scale oriented horizontally
to pull the block along the surface at a constant velocity to ensure the block remains in
equilibrium which, in turn resulting in the friction force being equal to the force seen on
the spring scale. When using a spring scale, make sure to use the one with the lowest
threshold until it is maxed out. This will ensure the most accurate data.
Goal: To determine if the factor your group is studying actually affects the friction force.
Predictions:
Here are some factors that might affect the friction force:
- Type of surface
- Surface area
- Weight of the object
- The object’s state of motion (at rest or already moving)
- The speed of the object
Materials: List everything you use here
Lab Setup: Draw what you actually did here
Procedure: List your step by step procedure that you ACTUALLY followed. (you don’t
need all of them) you should have multiple trials changing the tested variable while
keeping all other factors the same!
Data: Fill out whatever you need to in the table below (you don’t have to use the whole
table)
Factor
Procedure
Result and reason
Weight of object
Type of surface
Speed
1. pull block without weight
It does affect friction
2. read the number on the spring
because the percent
scale
difference with the weight is
3. pull block with weight and
and without the weight is
read number on spring scale
over 10%
1. place weight in block and
It does affect friction
attach spring scale to block
because there’s a 50%
2. drag block without paper and
difference
take measurements
3. drag block along sandpaper and
take measurements
1. attach the spring to the block
Speed affects friction force
2. pull block slowly
because percent difference
3. pull block fast
is 60%
Surface area
1. put it down flat and pull across
surface
2. read scale
3. pull tall and pull across surface
It does affect friction
because percent difference
50%
Objects state of
motion
1. pull slowly on the spring scale
and read before block moves
2. measure spring scale after the
block begins to move
Object’s state of motion
does affect friction because
the percent difference is
over 10%
Conclusion:
Based on the information presented, the friction force only depends on
______________________ , ______________________, and
_____________________________. The formula for the friction force is
________=_____ x__________. The factors that did not affect friction were
________________________ and ________________________________. Some
sources of error were ____________________________________________________
_______________________________________________________________________.
A future experiment could be _______________________________________________
________________________________________________________________________
_______________________________________________________________________.
Example: show all work including formula and substitution with units.
What force is needed to start a 20kg steel
What force is needed to keep that block
block sitting on a steel surface?
moving?