Friction (Alanna Martin)

Title:

Surface Friction Lab: the force of friction

Principle(s) Investigated:

Force, Friction (static and kinetic), (balanced and unbalanced)

Standards :

Forces

2. Unbalanced forces cause changes in velocity. As a basis for understanding this concept:

a. Students know a force has both direction and magnitude.

c. Students know when the forces on an object are balanced, the motion of the object does not change.

d. Students know how to identify separately the two or more forces that are acting on a single static object, including gravity, elastic forces due to tension or com­pression in matter, and friction.

e. Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down, or change direction).

Materials:

Tape, measuring tape, string, spring scales, wooden blocks, wooden blocks with sandpaper on the bottom, different surfaces

Procedure:

Each group will investigate four different surfaces (concrete floor, lab desk, lab floor, carpet) to test and collect data on surface friction.

1. Tie a piece of string firmly around each object (plain block of wood and the wood with sandpaper). Attach the looped end of the string to the spring scale.
2. Attach the 50 cm measuring line to your surface. The front will be your starting line and the end will be your finish line.
3. Pull the plain wood block across your assigned surface for the 50 cm at a SLOW, STEADY SPEED. Record the force (in N) required to pull the object.
4. Repeat step 3 two more times. Record your results.
5. Pull the wood block with sandpaper on the bottom across your assigned surface for the 50 cm at a SLOW, STEADY SPEED. Record the force (in N) required to pull the object.
6. Repeat step 5 two more times. Record your results below and on the class data spreadsheet.
   1. REPEAT STEPS 1-6 FOR EACH SURFACE!

As a class we will combine our data in a spreadsheet and interpret our data.

Enter your data here.

Student prior knowledge:

Students will need to know what a force is. A force is a push or a pull that has direction and magnitude. Students will need to know that forces are measured with Newtons. Students will need to know how to draw force arrows. Students will need to know about kinetic and static friction.

Explanation:

In this lab experiment, students investigate the roles that different surfaces play in effecting the force of friction.

Give a thorough explanation of the experiment or demonstration. Your explanation should be written to give your fellow teachers a solid understanding and include greater detail than what you might provide for your secondary students. Make certain to include equations whenever pertinent.

Questions & Answers:

How does friction help us walk? Do we need friction to be able to walk?

-Yes, we need friction to be able to walk. Without friction, our feet/ shoes would slide on all surfaces.

Would humans be able to make a fire by rubbing sticks together without friction?

- No, without friction we would not be able to make fire in this way. The friction between two sticks converts kinetic energy to thermal/ heat energy. The two sticks act as a fuel, oxygen is provided from the air and the friction from rubbing the sticks together makes heat. These components act together to create fire.

Friction slows things down, would it be better if there was no friction in the world?

-No, the world needs friction to function as we know it. Friction does make it harder to move your couch across the floor (especially if it is carpeted) when rearranging your furniture; however, we need friction to perform most of our daily activities.

Applications to Everyday Life: Explain (don't just list) three instances where this principle can be used to explain other phenomenon.

Life would be very different without friction. Friction allows us to do many things we might take for granted. Friction allows us to walk, run, ride a bike, stop our car while driving. Without friction we would be slipping, sliding and falling all over.

Without friction, we would be unable to grip or hold on to anything. Friction allows us to write. Friction allows us to hold a pencil because the force of gravity wants to pull the pencil down, however the force of friction opposes this movement and allows us to grip the pencil.

Without friction humans wouldn't be able to make fire by rubbing sticks together. The invention of fire allowed early humans to cook their food.

Photographs:

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