Scientific Question
How does the size of sand in sandpaper affect the static friction between it and the surface it
rubs against?
Background Information
Forces are pushes and pulls applied to objects that can cause a change in motion. Forces are
measured in Newtons (N) which is just about equal to the force gravity exerts on a 100g object.
Friction is a type of force that resists motion when two objects come into contact with one
another. Static friction is a type of friction that occurs between two objects that are in contact
but are not in motion. The smoother a surface is, the less friction it will exert.
Source: The Push and Pool of Forces by Professor Isaac Newton XII,
Sandpaper is a form of paper where an abrasive material has been fixed to its surface. The size
of the particles of sand is referred to as its Grit Size. In the U.S. we use the CAMI grit size
system where the larger the CAMI number, the smaller the grit size.
Source: Sandpaper For Dummies by Gritty McGrit
Hypothesis
Based on my research, I believe that the sandpaper with the larger grit will generate less
friction because there will be less material touching between objects.
Materials
Materials:
1 100g wooden block w/hook
3 pieces of 24, 220, 500 grit sand paper
1 metric spring scale
Experimental Procedure
I will fasten one piece of 24 grit sandpaper to the table top with masking tape. Then I will place
the 100g block in the center of the piece of 24 grit sand paper. I will then attach the spring
scale to the 100g block. I will then pull the spring scale horizontally until the block begins to
move. I will record how many grams the spring scale read the instant the block moved. I will
record the data in my data table. I will then convert grams into Newtons by dividing the
number of grams by 100. I will repeat this process two more times using a new piece of sand
paper each time. I will then find the average for my three trials and record that in my data
table as well.
I will fasten one piece of 220 grit sandpaper to the table top with masking tape. Then I will
place the 100g block in the center of the piece of 220 grit sand paper. I will then attach the
spring scale to the 100g block. I will then pull the spring scale horizontally until the block begins
to move. I will record how many grams the spring scale read the instant the block moved. I will
record the data in my data table. I will then convert grams into Newtons by dividing the
number of grams by 100. I will repeat this process two more times using a new piece of sand
paper each time. I will then find the average for my three trials and record that in my data
table as well.
I will fasten one piece of 500 grit sandpaper to the table top with masking tape. Then I will
place the 100g block in the center of the piece of 500 grit sand paper. I will then attach the
spring scale to the 100g block. I will then pull the spring scale horizontally until the block begins
to move. I will record how many grams the spring scale read the instant the block moved. I will
record the data in my data table. I will then convert grams into Newtons by dividing the
number of grams by 100. I will repeat this process two more times using a new piece of sand
paper each time. I will then find the average for my three trials and record that in my data
table as well.
Results
Force Needed to Move 100g Wooden Block
CAMI Grit
Trial 1 (g)
Trial 1 (N)
Trial 2 (g)
Trial 2 (N)
Trial 3 (g)
Trial 3 (N)
AVG (N)
24
500
5
550
5.5
450
4.5
5
220
250
2.5
225
2.25
275
2.75
2.5
500
100
1
95
0.95
105
1.05
1
Conclusion
Based on my data it took an average of 5N to move the wooden block across 24 grit sandpaper
as opposed to 2.5N on 220 grit, and 1N on 500 grit sandpaper. This disproves my hypothesis
because the smaller grit sandpaper required less force to move the wooden block than the
larger grit which means that it exerted less friction on the block. I believe that this is because
the smaller grit sandpaper is smoother than the larger grit sandpaper. I believe these results
are accurate and unbiased. The one thing I can do to improve my results if this test was done
again is to use more grit sizes to increase the amount of data I collect.
Application
I believe that this experiment can be applied in many important situations. One situation is in
the types of roads we build and the safety involved. For example, on streets with a lot of stop
and go traffic, we can incorporate small stones to keep the streets from being completely
smooth to increase the friction between the roads and a vehicles tire. This will help a vehicle
stop sooner and will provide more traction when maneuvering. We can also apply this to
freeways where vehicles do not stop as often by making these roads as smooth as possible. By
doing so, we will decrease the amount of friction between the vehicle and the road which
would result in better gas mileage.