Lab 4 Friction PHY250L
Student Name:
Access Code (located on the underside of the lid of your lab kit):
Lab Report Format Expectations
Utilize college level grammar and formaṄng when answering text based questions.
Report all equations in a proper mathematical format, with the correct signs and symbols.
Submissions with incomplete or improperly formatted responses may be rejected.
Pre-Lab Questions
1. This lab contains two different experiments that cover two different aspects of friction. In your
own words, describe both concepts and how each experiment demonstrates them.
This lab has two different experiments: one focuses on static friction, which is the force that
keeps something from moving when you first try to push it. The other experiment is about what
happens once things are already moving and sliding around. In the first experiment, you see
how much force it takes to just barely get something moving. In the second, you measure the
force needed to keep it moving at a steady speed. This shows the difference between how
friction works before and after things start to move.
2. The normal force plays an important role when studying friction. Describe the relationship
between friction and the normal force.
The normal force is really just how hard something is sitting or leaning on whatever’s
underneath it. If something’s heavier, it pushes down more, and that means there’s more
friction too. So, if you press down harder or if the object is heavier, friction increases by the
same amount.
EXPERIMENT 1: STATIC FRICTION AND MASS ON AN INCLINE PLANE
Introduction Questions
1. Explain, generally, what you will do for Experiment 1.
In this experiment, I’ll place an object on a ramp and slowly raise one end until the object just
starts to slide. I’ll record the angle where it begins to move.
2. If the normal force only acts perpendicular to a surface, what happens to the magnitude of the
normal force on an object as the angle of the incline is increased?
As the angle of the ramp gets steeper, the normal force gets smaller. This is because less of the
object’s weight is pressing straight down into the surface, so the support force from the ramp
decreases as you tilt it more.
, Lab 4 Friction PHY250L
3. Applying Newton’s Second Law and the equation for static friction (F = μsN), we can prove that
the coefficient of static friction (μs) is related to the minimum angle, θ, that causes the block to
slip (see Figure 5) by the equation μs = tan(θ). Starting with the knowledge that the total force
on an object is the force acting in one direction, minus the force of friction which opposes it:
Fnet = Facceleration - Ffriction
solve for this relationship - μs = tan(θ). Hint: Break this down into the x and y components of
sin( θ )
force and remember the trigonometric identity tan ( θ )= .
cos( θ )
μₛ = tan(θ)
In other words, the number you get for friction matches the tangent of the angle where the
block finally starts sliding.
Figure 5: A block slipping down a ramp.
4. Suppose you know the coefficient of static friction, and you want to solve for the minimum
angle from the equation μs = tan(θ). How can you solve for θ, here?
θ = arctan(μₛ)
This means you take the inverse tangent (arctan) of the coefficient of static friction to find the
minimum angle.
Student Name:
Access Code (located on the underside of the lid of your lab kit):
Lab Report Format Expectations
Utilize college level grammar and formaṄng when answering text based questions.
Report all equations in a proper mathematical format, with the correct signs and symbols.
Submissions with incomplete or improperly formatted responses may be rejected.
Pre-Lab Questions
1. This lab contains two different experiments that cover two different aspects of friction. In your
own words, describe both concepts and how each experiment demonstrates them.
This lab has two different experiments: one focuses on static friction, which is the force that
keeps something from moving when you first try to push it. The other experiment is about what
happens once things are already moving and sliding around. In the first experiment, you see
how much force it takes to just barely get something moving. In the second, you measure the
force needed to keep it moving at a steady speed. This shows the difference between how
friction works before and after things start to move.
2. The normal force plays an important role when studying friction. Describe the relationship
between friction and the normal force.
The normal force is really just how hard something is sitting or leaning on whatever’s
underneath it. If something’s heavier, it pushes down more, and that means there’s more
friction too. So, if you press down harder or if the object is heavier, friction increases by the
same amount.
EXPERIMENT 1: STATIC FRICTION AND MASS ON AN INCLINE PLANE
Introduction Questions
1. Explain, generally, what you will do for Experiment 1.
In this experiment, I’ll place an object on a ramp and slowly raise one end until the object just
starts to slide. I’ll record the angle where it begins to move.
2. If the normal force only acts perpendicular to a surface, what happens to the magnitude of the
normal force on an object as the angle of the incline is increased?
As the angle of the ramp gets steeper, the normal force gets smaller. This is because less of the
object’s weight is pressing straight down into the surface, so the support force from the ramp
decreases as you tilt it more.
, Lab 4 Friction PHY250L
3. Applying Newton’s Second Law and the equation for static friction (F = μsN), we can prove that
the coefficient of static friction (μs) is related to the minimum angle, θ, that causes the block to
slip (see Figure 5) by the equation μs = tan(θ). Starting with the knowledge that the total force
on an object is the force acting in one direction, minus the force of friction which opposes it:
Fnet = Facceleration - Ffriction
solve for this relationship - μs = tan(θ). Hint: Break this down into the x and y components of
sin( θ )
force and remember the trigonometric identity tan ( θ )= .
cos( θ )
μₛ = tan(θ)
In other words, the number you get for friction matches the tangent of the angle where the
block finally starts sliding.
Figure 5: A block slipping down a ramp.
4. Suppose you know the coefficient of static friction, and you want to solve for the minimum
angle from the equation μs = tan(θ). How can you solve for θ, here?
θ = arctan(μₛ)
This means you take the inverse tangent (arctan) of the coefficient of static friction to find the
minimum angle.
