Physics 111A - Lab Report
Lab 106: Static and Kinetic Friction
Introduction
The purpose of this experiment is to explore static and kinetic friction between two surfaces. We
aim to find the coefficient of static (μs) and kinetic friction (μk). We use a friction cart and
analyze the forces acting on it using free body diagrams and confirm our theoretical procedures
by our experimental results. Friction is the opposing force acting between two surfaces. There
are two types of friction forces: Static friction, which prevents motion till a certain limit and
Kinetic friction, which is an opposing force that stops motion after it has started. The forces
transition from static and kinetic force is distinguished by different magnitudes of friction forces.
Theoretical Background
Friction primarily arises from the interaction between two surfaces in contact, acting parallel to
them. It resists any relative motion between the surfaces, opposing the direction of movement.
The magnitude of frictional force is equal in magnitude but opposite in direction to any exerted
force. When the object is static, the exerted force is less than the frictional force, which in this
case is called the static frictional force. When the object is in motion, the exerted force is greater
than the frictional force and the force is called kinetic friction force. At the threshold, the block is
on the limit of moving and the magnitude of the static friction force is maximum. After this the
friction force is considered as kinetic friction.
The static friction is described by
𝑓𝑠 = µ𝑠𝑁 , 0 < fs ≤ fs, max
where N is the normal force acting perpendicular to the surface
Once our object begins to slide, the kinetic friction is described by
𝑓𝑘 = µ𝑘𝑁
Both the equations display a linear relation between friction and normal forces where both forces
are directly proportional to each other.
In our experiment, we analyze the friction forces acting on a cart. We measure the static force,
the force required to move the cart, and kinetic force, the force that keeps the cart in constant
velocity. Then we use the values to calculate the coefficients. We also investigate the critical
angle, which is the angle at which the cart transitions from static to kinetic friction.
, Procedure
The Equipment used in our experiment is:
- Data Collection System
- Wireless bluetooth Smart Cart
- Plastic Friction Cart
- Dynamic Track
- Elastic Bumper
- Track End Stop
- Pulley with a clamp
- Tripod Stand
- Cart Mass
- Digital Protractor
- Mass and hanger set
- String
- Balance
Set Up
Part 1: Determining the static and kinetic friction coefficients
Set up the track and attack your friction cart using a string. Weigh the cart and record the value in
a table. Connect the cart to the data collection system. Once the cart is securely attached, we
begin our experiment. Both the carts are placed next to each other and the smart cart is pulled at
a constant velocity till the string is pulled taut and the friction cart starts moving. We press
‘Record’ before we begin moving the cart and end our recording after both the carts move at a
constant velocity for a moment. We use the readings on our software to record the mean kinetic
friction force and the maximum static friction force. Repeat this process with 2, 3 and 4 cart
masses.
Part 2: Determining the critical angle of an inclined plane for a cart to begin sliding down
First, we set up the equipment required for the experiment. The starting end of the track is
elevated on a tripod stand. The friction cart is placed on the track and mass is placed inside the
track. The track is raised till it reaches a point where the cart slowly slides down. The angle at
which the cart begins to slide is considered the critical angle. The angle is recorded using the
digital protractor. The experiment is repeated 4 more times, with the mass increasing each time.
The critical angle for all 5 trials is recorded on a table and the static coefficient friction is
measured using the equation
µ𝑠 = 𝑡𝑎𝑛θ𝑐, where θc is the critical angle
Part 3: Predict the Acceleration of a Cart on a Horizontal Plane with friction
Set up the track and the rest of the equipment required. Place the elastic bumper on the finishing
end of the track. Ensuring the track is horizontal is a crucial step. Make sure the rubber bands are
properly installed to ensure the vehicle comes to a stop instead of being derailed off the track.
Attach a pulley to the end of the card and place a measured amount of hanging mass onto the
pulley. The smart cart is attached to the friction cart using a string which is attached to the
hanging mass using another string. Place mass onto the cart. Press record on the measurement
Lab 106: Static and Kinetic Friction
Introduction
The purpose of this experiment is to explore static and kinetic friction between two surfaces. We
aim to find the coefficient of static (μs) and kinetic friction (μk). We use a friction cart and
analyze the forces acting on it using free body diagrams and confirm our theoretical procedures
by our experimental results. Friction is the opposing force acting between two surfaces. There
are two types of friction forces: Static friction, which prevents motion till a certain limit and
Kinetic friction, which is an opposing force that stops motion after it has started. The forces
transition from static and kinetic force is distinguished by different magnitudes of friction forces.
Theoretical Background
Friction primarily arises from the interaction between two surfaces in contact, acting parallel to
them. It resists any relative motion between the surfaces, opposing the direction of movement.
The magnitude of frictional force is equal in magnitude but opposite in direction to any exerted
force. When the object is static, the exerted force is less than the frictional force, which in this
case is called the static frictional force. When the object is in motion, the exerted force is greater
than the frictional force and the force is called kinetic friction force. At the threshold, the block is
on the limit of moving and the magnitude of the static friction force is maximum. After this the
friction force is considered as kinetic friction.
The static friction is described by
𝑓𝑠 = µ𝑠𝑁 , 0 < fs ≤ fs, max
where N is the normal force acting perpendicular to the surface
Once our object begins to slide, the kinetic friction is described by
𝑓𝑘 = µ𝑘𝑁
Both the equations display a linear relation between friction and normal forces where both forces
are directly proportional to each other.
In our experiment, we analyze the friction forces acting on a cart. We measure the static force,
the force required to move the cart, and kinetic force, the force that keeps the cart in constant
velocity. Then we use the values to calculate the coefficients. We also investigate the critical
angle, which is the angle at which the cart transitions from static to kinetic friction.
, Procedure
The Equipment used in our experiment is:
- Data Collection System
- Wireless bluetooth Smart Cart
- Plastic Friction Cart
- Dynamic Track
- Elastic Bumper
- Track End Stop
- Pulley with a clamp
- Tripod Stand
- Cart Mass
- Digital Protractor
- Mass and hanger set
- String
- Balance
Set Up
Part 1: Determining the static and kinetic friction coefficients
Set up the track and attack your friction cart using a string. Weigh the cart and record the value in
a table. Connect the cart to the data collection system. Once the cart is securely attached, we
begin our experiment. Both the carts are placed next to each other and the smart cart is pulled at
a constant velocity till the string is pulled taut and the friction cart starts moving. We press
‘Record’ before we begin moving the cart and end our recording after both the carts move at a
constant velocity for a moment. We use the readings on our software to record the mean kinetic
friction force and the maximum static friction force. Repeat this process with 2, 3 and 4 cart
masses.
Part 2: Determining the critical angle of an inclined plane for a cart to begin sliding down
First, we set up the equipment required for the experiment. The starting end of the track is
elevated on a tripod stand. The friction cart is placed on the track and mass is placed inside the
track. The track is raised till it reaches a point where the cart slowly slides down. The angle at
which the cart begins to slide is considered the critical angle. The angle is recorded using the
digital protractor. The experiment is repeated 4 more times, with the mass increasing each time.
The critical angle for all 5 trials is recorded on a table and the static coefficient friction is
measured using the equation
µ𝑠 = 𝑡𝑎𝑛θ𝑐, where θc is the critical angle
Part 3: Predict the Acceleration of a Cart on a Horizontal Plane with friction
Set up the track and the rest of the equipment required. Place the elastic bumper on the finishing
end of the track. Ensuring the track is horizontal is a crucial step. Make sure the rubber bands are
properly installed to ensure the vehicle comes to a stop instead of being derailed off the track.
Attach a pulley to the end of the card and place a measured amount of hanging mass onto the
pulley. The smart cart is attached to the friction cart using a string which is attached to the
hanging mass using another string. Place mass onto the cart. Press record on the measurement
