Friction (µ)

Enduring Understanding:

At the macroscopic level, forces can be categorized as either long-range (action-at-a-distance) forces or contact forces.

3.C.4 Contact forces result from the interaction of one object touching another object, and they arise from interatomic electric forces. These forces include tension, friction, normal, spring (Physics 1), and buoyant (Physics 2).

3.C.4.1 Make claims about various contact forces between objects based on the microscopic cause of these forces. [SP 6.1]
3.C.4.2 Explain contact forces (tension, friction, normal, buoyant, spring) as arising from interatomic electric forces and that they therefore have certain directions.

TED Radio Hour - FrictionWe encounter friction every day—in all its forms—as we brush our teeth, go for a jog, argue with a friend. This hour, TED speakers explore how this force can be dialed up or down to improve our lives. Guests include tribologist Jennifer Vail, democracy activist Yaël Eisenstat, Sierra Leone's Minister of Education David Moinina Sengeh, and TV producer Elan Gale.

Great Podcast about different ideas of Friction in our daily lives:

0 - 15 min - Mechanical Friction (focus of this class)

15 - 30 min - Friction in our Online World - How can social media sites implement some friction to control political discourse?

30 - 45 min - Friction in Reality TV - Not a fan of reality TV so I didn't listen to this part...

How do the various materials (various µ) affect the sound of the gong?

Motorcycle vs. a Truck

A motorcycle and large transport truck are traveling at the same speed on a busy highway. Ahead is a traffic jam and both drivers need to stop their vehicles in 100 meters or they will crash into the back of the stopped cars ahead of them. They both slam on their brakes at the same time and SKID to a stop. Suppose the tires of the motorcycle and truck are made of the same material and both are traveling at the same velocity.

The motorcycle stops just before hitting the cars, predict where the truck would stop.

Block on a Ramp w/ Friction

How do the forces of Force Normal and Force Friction change as the angle of a ramp is increased from 0˚ to 90˚?

What is the relationship between the Force Friction and Force Normal on the ramp.

Factors Affecting the Force of Friction

Two ways to friction:

Using a Force sensor, drag a block across a surface.
1. What variables can you vary?
2. How will you record quantitative data (5 treatments x3 trials)?
Using a inclined plane, raise the plane until the block starts to slide. Adjust the ramp to allow the block to slide at a constant speed.
1. What variables can you vary?
2. How will you record quantitative data?

Forces Acting on a Plane Background - The Physics Classroom

Collins Physics and More - D.R.A.C. D - DATA

Clayton Physics Resources - Graphical Analysis Guide Graphical analysis is a vital skill in any scientists tool belt! Understanding how to create and interpret a graph allows you to dive into a deep exploration and how it works. This guide was written to help physics students learn how to collect data in an organized and systematic way, graph that

Data Analysis:

GROUP -
1. Collect sufficient data to draw a conclusion.
2. 5 treatments of the IV with a minimum of 3 trials for each treatment
INDIVIDUALLY -
1. Process the raw data you collected.
2. Graph the results of your data.
3. Compare your results to the theoretical concept of friction.
4. Draw any conclusions regarding your IV and DV.

Sample Problems

Sample Problem 1:

A 5 kg box on a horizontal table is pushed by a horizontal force of 15 N as shown on the right. If the coefficient of friction is 0.4, will the box move? Justify your answer.

Sample Problem 2:

One end of a light inextensible string is attached to a tool box of mass 2.5 kg which is lying on a horizontal table. The string passes over a smooth pulley and is tied at the other end to a bag of mass 1.4 kg.

Draw a diagram showing the forces acting on the tool box.
If the tool box is just on the point of sliding, find a value for μ, the coefficient of friction.

Spiral Conveyor Belts:

At an Amazon warehouse, a conveyor belt is used to carry boxes up a spiral conveyor belt from one part of a factory to another. For this particular processing line the cardboard boxes range in mass from 0.5 kg to 10.0 kg. The μ = 0.55 and each box is just on the point of sliding,

Find the frictional force acting on a 5.0 kg box.
Determine the maximum angle the spiral conveyor belt could have to move the boxes from one level to another.

Additional Resources:

Friction Model:

Three brass masses, labeled A, B and C, have masses of 0.1kg, 0.2kg and 0.3kg respectively. They were placed on a sheet of paper

From the information in the GIF to the left, suggest a model that will explain the observed phenomena.

Determine the µ(s) of between the masses and paper.

PhET Friction Simulation

The Entire Flipping Physics FRICTION Video Series

[2] (4:59) Introduction to the Coefficient of Friction
[2] (6:58) Understanding the Force of Friction Equation
[2] (2:57) Experimentally Graphing the Force of Friction
[3] (7:59) Does the Book Move? An Introductory Friction Problem
[1] (4:39) Do Anti-lock Brakes use Static or Kinetic Friction? by Billy
[3] (9:19) A Friction Review Problem - The Original Billy Bobby and Bo
[2] (2:57) Everybody Brought Mass to the Party!
[3] (8:59) Determining the Static Coefficient of Friction between Tires and Snow
[3] (6:35) Breaking the Force of Gravity into its Components on an Incline
[3] (9:22) Physics "Magic Trick" on an Incline
[3] (6:41) Introductory Static Friction on an Incline Problem
[2] (2:34) Calculating the Uncertainty of the Coefficient of Friction
[3] (6:59) Introductory Kinetic Friction on an Incline Problem

Better to Push or Pull?

A contestant in a winter sporting event pushes a 45.0-kg block of ice across a frozen lake as shown.

Calculate the minimum force 𝐹 he must exert to get the block moving.
What is the magnitude of its acceleration once it starts to move, if that force is maintained?
How would the forces and accelerations differ if the contestant were pulling the block of ice with a rope over his shoulder at the same angle above the horizontal as shown in (b).

Solutions

Calculating Force Friction on a Ramp (and possible acceleration)

A skier with a mass of 62 kg is sliding down a snowy slope at a constant speed.

Determine the force friction acting on the skier.
Determine the coefficient of friction between the skis and snow.
Suppose the mass of the skier were to double. Express the force friction in terms of m, θ, and any physical constants as necessary.
1. How does this affect the coefficient of friction?
The skier is approaching an icy patch on the slope, how will this affect their motion as they travel down the hill (at the same angle)?

Solutions

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