physics project on static friction

1. INTRODUCTION
Friction is a resistive force that occurs due to motion between
two contacting surfaces. The two surfaces must either be
sliding or attempting to slide over another resulting in a force
that is tangent to the two surfaces and in a direction that
tends to oppose the motion of each surface. In general,
frictional force depends on the nature and physical properties
of the surfaces in contact. It slows down the motion of an
object and is directed along the two surfaces in contact in the
opposite direction of the motion. Friction is always called a
non-conservative force because some energy is needed to
overcome it.
The following conclusions can be made of friction, Friction
between two surfaces is:
Independent of the surface area of contact
Independent of the sliding speed of the surfaces
Proportional to the normal force acting on the surfaces
Acts in a direction opposite to the direction of motion of each
surface.

2. Types of Friction
There are different types of friction. A book moving across the
desk is an example of sliding friction. As the book slides cross
the desk, the bottom of the book is touching the desk. The
source of the friction is the contact between the surface and the
book and the desk. The weight of the object and the type of
surface it moves over determine the amount of sliding friction
present between the two objects. A heavy object exerts more
pressure on the surface is slides over, so the sliding friction
will be greater.
Air, water and oil are all fluids. Air resistance is a type of
fluid friction. As

3. an object falls, air resistance pushes it up on the object.
When you ride a bicycle, the contact between the wheel and
the road is an example of rolling friction. When an object rolls
over a surface, the force needed to overcome rolling friction is
much less than that needed to overcome sliding friction.
Kinetic Friction
When you moved your book across the desk, the book
experience a type of friction that acts on moving objects.
This force is known as a kinetic friction force. It is exerted on
one surface by another when the two surfaces rub against
each other because one or both surfaces are moving. If you
stack additional books on top of the first book to increase
the normal force, the kinetic friction force will increase.
Let's look at the formula for kinetic friction force.
There is a linear relationship between the kinetic friction
force and the normal force. The coefficient of kinetic friction
relates the friction force to the normal force. The kinetic
friction force (F(f, kinetic)) equals the product of the
coefficient of kinetic friction (µ(k)) and the normal force
(F(N)). F(f, kinetic) = µ(k) * F(N)

4. Static Friction
Imagine trying to push a couch across the floor. You push on
it with a small force, but it does not move. This is because it
is not accelerating. Newton's laws tell you that the net force
on the couch must be zero. There must be a second
horizontal force acting on the couch, one that opposes your
force and is equal in size. This force is static friction force,
which is the force exerted on the surface by another when
there is no motion between the two surfaces.
Static friction force acts in response to a force trying to cause
a stationary object to start moving. If there is no such force
acting on an object, the static friction force is zero. If there
is a force trying to cause motion, the

5. static friction force will increase up to a maximum value
before it is overcome and motion starts.
The maximum static friction force relates to the normal force
in a similar way as the kinetic friction force. In the equation
for maximum static friction force, µ(s) is the coefficient of
static friction between two surfaces. The maximum static
friction force that must be overcome before motion can
begin is µ(s) * F(N). In the example of pushing the couch, the
maximum static friction force balances the force of the
person pushing on the couch the instant before the couch
begins to move.

6. Causes of Friction
All surfaces, even those that appear to be smooth, are rough
at a microscopic level. If you look at a photograph of a
graphite crystal magnified by a scanning tunneling
microscope, the atomic level surface irregularities of the
crystal are revealed. When two surfaces touch, the high points
on each are in contact and temporarily bond. This is the origin
of friction.
Measuring Coefficients of Friction
On what does a friction force depend? The materials that the
surfaces are made of play a role. For example, imagine trying
to play basketball while wearing socks instead of athletic
shoes. You would slip and slide all over the basketball court.
Shoes help provide the forces necessary to quickly change
directions while running up and down the court. There is more
reaction between your shoes and concrete than there is
between your socks and a polished wood floor.

7. This table shows coefficients of static friction (µ(s)) and
coefficients of kinetic friction (µ(k)) between various
surfaces.
The coefficients of friction show how easily one object can
slide against another.
These coefficients are estimates for each combination
of surfaces. Exact
measurements of coefficients of friction are quite sensitive
to the conditions of the surfaces and are determined
experimentally.
Another important fact regarding the table is that all the
measurements were made on dry surfaces (with exception
of the oiled steel). Wet surfaces behave quite differently
than dry surfaces.
≤µs n.

8. THEORY:
There are two types of frictional forces:
a) Static friction ( fs)
This exists when the object is at rest relative to the surface. This
force must be overcome in order to make the object start
moving. It is given by fs

9. 0BJECTIVE
the nature of the frictional force between
two wooden surfaces will be
investigated. This will lead to the
observation of the properties of friction.
The following objectives will be
accomplished:
1. the determination of the coefficients of static friction, µs
, between two wood surfaces by sliding the block down
the board.
2. Determination of the coefficient of friction by using the
board as
3. Comparison of the four values of µs from the four
different methods.
4. Demonstration that the coefficients of friction are
dependent of the surface area of contact.

10. MATERIALS
1.Wooden Block
2.Weight hanger
3.Wooden Board
4.Slotted weights
5. balance
6.Pulley
7..String
8.Paper towel
9. Two sheets of Cartesian graph
paper

11. EXPERIMENTAL PROCEDURE
For simple surface onlyFor simple surface only
1. Weigh the wooden block on the triple beam
balance and record its weight
2. Set up the block on the board with the largest
surface in contact with the board surface
and string attached to the block run over a
pulley. Place some weights on the weight
hanger. Slightly increase the load on the
weight hanger until the block begins to
move slowly with a constant speed after it has
been started with a very small

12. push. Make sure you wipe away any dust from the surfaces.
Record the weight placed on the weight hanger including
the mass of the weight hanger. 200 g on the surface of
the block. Slowly increase the load on the hanger until
the block starts slowly moving with constant speed after
given a small push. Don’t forget to include the mass of
the hanger.
3. Repeat Procedure 2 above placing masses of 200,
400, 600, 800 and 1000 g successively on top of the wood
block. Record the total weights placed on the weight
hanger including the weight hanger. The coefficient of
kinetic friction can be obtained from these data.
4. Turn and place the smallest side of the wood block on
the board and repeat Procedure 2 above.
5. Set up the block again as in procedure 2 and place a
mass of 600 g on it. Place weights gently on the hanger and
increase them slowly until the block just starts its motion
without any push. Repeat a total of 3 independent trials
and record your data. With this data you can find the
coefficient of static friction

13. REPORT FORM
Weight of block
Weight of pan
µk from graph ________
Weight on
block
Weight on pan Weight of
pblock +weight
on block
Weight of
pan+weight on
pan

14. EXPERIMENTAL PROCEDURE
For sandy surface onlyFor sandy surface only
1. Weigh the wooden block on the triple beam
balance and record its weight
2. Set up the block on the board with the largest
surface in contact with the board surface
and string attached to the block run over a
pulley. Place some weights on the weight
hanger. Slightly increase the load on the
weight hanger until the block begins to
move slowly with a constant speed after it has
been started with a very small

15. push. Make sure you wipe away any dust from the surfaces.
Record the weight placed on the weight hanger including
the mass of the weight hanger. 200 g on the surface of
the block. Slowly increase the load on the hanger until
the block starts slowly moving with constant speed after
given a small push. Don’t forget to include the mass of
the hanger.
3. Repeat Procedure 2 above placing masses of 200,
400, 600, 800 and 1000 g successively on top of the wood
block. Record the total weights placed on the weight
hanger including the weight hanger. The coefficient of
kinetic friction can be obtained from these data.
4. Turn and place the smallest side of the wood block on
the board and repeat Procedure 2 above.
5. Set up the block again as in procedure 2 and place a
mass of 600 g on it. Place weights gently on the hanger and
increase them slowly until the block just starts its motion
without any push. Repeat a total of 3 independent trials
and record your data. With this data you can find the
coefficient of static friction

16. REPORT FORM
Weight of block
Weight of pan
µk from graph ________
Weight on
block
Weight on pan Weight of
pblock +weight
on block
Weight of
pan+weight on
pan

17. EXPERIMENTAL PROCEDURE
For oily surface onlyFor oily surface only
1. Weigh the wooden block on the triple beam
balance and record its weight
2. Set up the block on the board with the largest
surface in contact with the board surface
and string attached to the block run over a
pulley. Place some weights on the weight
hanger. Slightly increase the load on the
weight hanger until the block begins to
move slowly with a constant speed after it has
been started with a very small

18. push. Make sure you wipe away any dust from the surfaces.
Record the weight placed on the weight hanger including
the mass of the weight hanger. 200 g on the surface of
the block. Slowly increase the load on the hanger until
the block starts slowly moving with constant speed after
given a small push. Don’t forget to include the mass of
the hanger.
3. Repeat Procedure 2 above placing masses of 200,
400, 600, 800 and 1000 g successively on top of the wood
block. Record the total weights placed on the weight
hanger including the weight hanger. The coefficient of
kinetic friction can be obtained from these data.
4. Turn and place the smallest side of the wood block on
the board and repeat Procedure 2 above.
5. Set up the block again as in procedure 2 and place a
mass of 600 g on it. Place weights gently on the hanger and
increase them slowly until the block just starts its motion
without any push. Repeat a total of 3 independent trials
and record your data. With this data you can find the
coefficient of static friction

19. REPORT FORM
Weight of block
Weight of pan
µk from graph ________
Weight on
block
Weight on pan Weight of
pblock +weight
on block
Weight of
pan+weight on
pan

20. EXPERIMENTAL PROCEDURE
For greasy surface onlyFor greasy surface only
1. Weigh the wooden block on the triple beam
balance and record its weight
2. Set up the block on the board with the largest
surface in contact with the board surface
and string attached to the block run over a
pulley. Place some weights on the weight
hanger. Slightly increase the load on the
weight hanger until the block begins to
move slowly with a constant speed after it has
been started with a very small

21. push. Make sure you wipe away any dust from the surfaces.
Record the weight placed on the weight hanger including
the mass of the weight hanger. 200 g on the surface of
the block. Slowly increase the load on the hanger until
the block starts slowly moving with constant speed after
given a small push. Don’t forget to include the mass of
the hanger.
3. Repeat Procedure 2 above placing masses of 200,
400, 600, 800 and 1000 g successively on top of the wood
block. Record the total weights placed on the weight
hanger including the weight hanger. The coefficient of
kinetic friction can be obtained from these data.
4. Turn and place the smallest side of the wood block on
the board and repeat Procedure 2 above.
5. Set up the block again as in procedure 2 and place a
mass of 600 g on it. Place weights gently on the hanger and
increase them slowly until the block just starts its motion
without any push. Repeat a total of 3 independent trials
and record your data. With this data you can find the
coefficient of static friction

22. REPORT FORM
Weight of block
Weight of pan
µk from graph ________
Weight on
block
Weight on pan Weight of
pblock +weight
on block
Weight of
pan+weight on
pan

23. CALCULATIONS
1) From procedure 2, draw a graph using the data of
the force of friction as the ordinate and those of the
normal force as the abscissas. Draw the best straight
line joining most of the points. Obtain the slope of
this graph. The slope so obtained is the coefficient of
kinetic friction, µk, between the wooden block and
board.
2 calculate the value for µs between block and board.
Find their average value and Compare the fourvalues
for µs for wood on wood,oil.san,grease
by calculating their percent difference which is given
by:
Percent difference = [difference of the two values/
average] x 100 %

24. Name of
surface
Wood and
wood
Wood and
oily surface
Wood and
greasy
surface
Woood and
sandy
surface
Percantage
e
difference