St. Joseph’s Secondary School
Grade 11 University Physics (SPH3U1)
Frictional Forces Lab
Purpose: The object of this lab is to find the coefficients of static friction ( s) and kinetic
friction (k), and to determine which (if any) of these variables affect friction: mass, gravity,
length, the normal force, etc. We will determine the coefficient of static friction between
the blocks and the counter (using several masses to vary the gravitational/normal forces).
We will also determine the coefficient of kinetic friction and compare it to static friction,
using similar masses.
Materials:
Friction Kits containing items like blocks (wood, metal), scales, rough surfaces, etc.
Masses and Scales
Protractors
Newton Spring Scales
String
Procedure:Part One:
(1) Using a friction block and mass, set up the
apparatus to measure horizontal friction. Start
with smaller masses and always place the
masses in the same place.
(2) Pull slowly on the mass horizontally until it
begins to move. What happens? Record the
force once the object starts moving.
(3) How much force do you need to keep the object moving? There are two types of
frictional force. Which is which?
(4) Repeat your procedure, adding larger masses each time. Record the frictional forces
(moving) each time. Try for at total of 3 masses.
(5) Plot a graph of frictional force F fr vs. normal force Fn. Describe its general shape.
What does the slope represent?
(6) What is the best k and s for your wooden block against the countertop?.
(7) Look at the table in the book for coefficients of friction and compare your values with
theirs. How close are your values to theirs?
Part Two:
(8) Measure a 30 degree angle between the ramp
and your horizontal surface. Repeat your procedure
from part one and determine the coefficients in this
case.
Conclusions/Discussion:
(1) Which kind of friction is greater and why?
(2) When friction is measured on a ramp at an angle,
what trigonometric quantity is the friction coefficient
equal to? Prove it, using a free body diagram.
(3) What is the relationship between friction and
mass for a horizontal surface?
(4) What are your sources of error for this experiment? How can they be reduced?
Data Tables: Part 1 (Level on Counter)
Trial
Masses
m (kg)
Force
Fg = mg
(N)
static:
1 mass
wood on
counter
2 mass
Normal
Force FN
FN = -mg
(N)
Applied
Force
Fapp from
Scale (N)
Friction
force Ffr
Ffr= -Fapp
(N)
Coefficient
= Ffr /FN
Average
Coefficient



3 mass
kinetic:
1 mass
wood on
counter
2 mass
3 mass
Data Tables: Part 2 (Inclined Plane, 30 degrees)
Trial
Masses
m (kg)
static:
1 mass
metal on
metal
2 mass
3 mass
kinetic:
1 mass
metal on
metal
2 mass
3 mass
Force
Fg =
mg
(N)
Normal Force
FN
FN = -mgcos
(N)
Applied
Force
Fapp
from
Scale (N)
Friction
force Ffr
Ffr= -Fapp
(N)
Coefficient
= Ffr /FN
Average
Coefficient


