Session 1: Feel the friction force

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Objective:  Identify from our life experience the friction force.

Explanation

Students all know intuitively the friction force concept. This session will make them feel through experiments the friction force.

They will also experience modification of parameters that influence the friction like for example the fluid.

Material

• Tanks full of water
• Apple
• Small and big racquets
• Racquets with  and without blocked holes
• Cars (toys)
• Piece of carpet

Maximum duration

30 minutes

Main question to be asked

• What is the friction force?
• Is the friction force helpful in our life?
• What is the difference between friction forces in solids and in fluids?

Introduction/Starters

Put an apple in a tank full of water and ask a student to put his/her  hands in his/her back then to grab the apple, with his mouth. What happens?

Then do the same experiments but put the apple on the table.

What is the difference?

Main activities

• Move your hand in the air. Do you feel something?
• Try the different small and big racquets, do the same
• Move your hand in the water
• Take a small racquet and move it in the tank of water

Discuss with your students about their interpretation of these experiments, and ask them to describe other life experiences where they have already experienced this feeling.

• Take small cars, ask them to roll on the floor
• Ask them to repeat the experiment with different materials on the floor

Ask your students what is the difference between this experiment with the car, and the experiments with the hand before.

Conclusion/Plenary

Friction forces will generate resistance to the displacement. In many application research is devoted to reducing these frictional forces.

There is a difference between the friction in a fluid and the contact friction between solids, but we have to keep in mind that we need friction forces to move and to stay on the floor while we are walking for example.

For example, in the case of a car when the car is moving it needs good tires, to have a good grip, but is also needs a good aerodynamic profile to reduce the friction forces to consume less fuel.

In the case of the plane, the wings are profiled in order to have a good lift but also to minimise frictional forces. When the plane is landing, the airbrakes placed on the end of the wings will be moved to increase the friction forces to slow down the plane.

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