KaiserScience

Home » Physics » Forces: Laws of Motion » Friction lab

Friction lab

friction lab 1

Lab groups will be assigned. Groups share data. Each person is responsible for typing up their own individual lab report.

Use 1” margins, Arial 12 point font, single spacing. Check your spelling and grammar.

Resource
This lab was adapted from https://www.fsd1.org/schools/westflorence/bgarey/Documents/Sample%20Lab%20Report.pdf

https://kaiserscience.wordpress.com/physics/forces/friction-lab/

 

Materials

Block of wood with an eye hook attached to one end.

Electronic or triple-beam balance

Spring scale calibrated in Newtons, grams, or both

4 100 gram slotted masses

Four uniform flat level surfaces, with varying coefficients of friction.

Conversion factors

The acceleration due to gravity, g, ≅ 10 m/s 2

What is the weight of a 1 kg mass?    Weight m x g  =  1 kg × 10 m/s 2  ≅ 1 0N

Thus these approximate conversions hold:

100kg ≅  1 kN (kiloNewton)           1 kg  ≅  10 N              0.1 kg  ≅  1 N

 

Procedure (repeat for each of the four surfaces)

Measure the mass of the wood block.

Use weight = m·g     Find it’s weight in Newtons.

Record weight on the sheet.

Hook your spring scale to the wood block. Very slowly, apply force until block begins to move.

Once moving, continue pulling at a constant speed – note the indicated force, and record.

Now add a 100 g mass to the block of wood

Hook your spring scale to the wood block. Very slowly, apply force until block begins to move.

Once moving, continue pulling at a constant speed – note the indicated force, and record.

Add a 2nd 100 g mass, repeat as above.

Add a 3rd  100 g mass, repeat as above.

Add a 4th  100 g mass, repeat as above.

Including the first measurement, we now have five data points.

 friction lab 2

Physics analysis

Since Σ F = 0 (sum of all forces equals zero)

then Σ x-forces should be zero    [all horizontal forces add up to zero.]

Also, Σ y-forces should be zero.  [all vertical forces add up to zero.]

Our pull (applied force) thus equals the frictional force. The normal force thus equals the weight.

Graphic analysis: Plot the force of friction vs the normal force

Use the applied force (pull) as the frictional force and weight as the normal force.

Determine a best fit line to fit the data points. Determine the slope of this line.

We will use the friction formula   Ff = μ·FN.  Note that this is the LINE formula, like y=m·x

Therefore slope equals  coefficient of friction for this surface.

Refresher lesson on finding slope here:

http://www.coolmath.com/algebra/08-lines/06-finding-slope-line-given-two-points-01

Friction lab data table

Write a brief conclusion, analyzing your results.

What did we learn?

Our data will not be perfect – what are the likely sources of experimental error?

Graph

Your graph will look something like this – except that we will have four lines. You can do this on your own with your preferred graphing software or app; or I can help you do this on a school computer with LoggerPro.

LoggerPro coefficient of friction

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework
HS-PS2-1. Analyze data to support the claim that Newton’s second law of motion is a
mathematical model describing change in motion (the acceleration) of objects when
acted on by a net force.

HS-PS2-10(MA). Use free-body force diagrams, algebraic expressions, and Newton’s laws of motion to predict changes to velocity and acceleration for an object moving in one dimension in various situations

A FRAMEWORK FOR K-12 SCIENCE EDUCATION: Practices, Crosscutting Concepts, and Core Ideas
PS2.A: FORCES AND MOTION
How can one predict an object’s continued motion, changes in motion, or stability?

Interactions of an object with another object can be explained and predicted using the concept of forces, which can cause a change in motion of one or both of the interacting objects… At the macroscale, the motion of an object subject to forces is governed by Newton’s second law of motion… An understanding of the forces between objects is important for describing how their motions change, as well as for predicting stability or instability in systems at any scale.

Massachusetts Science and Technology/Engineering Curriculum Framework (2006)

1. Motion and Forces. Central Concept: Newton’s laws of motion and gravitation describe and predict the motion of most objects.

1.4 Interpret and apply Newton’s three laws of motion.
1.5 Use a free-body force diagram to show forces acting on a system consisting of a pair of
interacting objects. For a diagram with only co-linear forces, determine the net force acting on a system and between the objects.
1.6 Distinguish qualitatively between static and kinetic friction, and describe their effects on the motion of objects.
1.7 Describe Newton’s law of universal gravitation in terms of the attraction between two objects, their masses, and the distance between them.
1.8 Describe conceptually the forces involved in circular motion.

%d bloggers like this: