2. Sailing into Physics Friction using Car and Ramp and the Engineering Design Cycle

3. Learning Goals  Use technology to measure and describe forces acting on a car in motion.  Define friction.  Distinguish among various types of friction.  Design a sail car that will slow down or speed up a car undergoing friction  Explain applications of friction.

4. Friction  Friction is a force that resists the motion of objects or surfaces.  Many kinds of friction exist.

5. Friction

6. Defining a “system”  First we need to see how a car responds to unbalanced forces and identify the types of friction.  Set up your equipment and let’s see what we variables we can control.

7. Setting up the experiment

9. Friction and two surfaces  Friction depends on both of the surfaces in contact.  When the hockey puck slides on ice, a thin layer of water between the rubber and the ice allows the puck to slide easily.

10. Friction and energy  Each time two moving surfaces touch each other, tiny bits of material are broken off by friction.  Breaking off bits of material uses energy.

11. Identifying friction forces  Friction is a force, measured in newtons just like any other force.

12.  Sliding friction is a force that resists the motion of an object moving across a surface. Identifying friction forces

13. Collect Data

14. Create the “Sail Car”

15. Make a hypothesis  If the sail is affected by air friction, then the car’s speed will:  a) slow down by ______ %  b) speed up by ______ %  c) stay the same

16. Collect Data for “Sail Car”

17. Analyze any % change in Average Speed due to Air Friction  % increase = Trial 1 – Trial 2 x 100% Trial 1  % decrease = Trial 2 – Trial 1 x 100% Trial 1

18. Friction and energy  Friction changes energy of motion into heat energy.

19. Reducing the force of friction  Unless a force is constantly applied, friction will slow all motion to a stop eventually.  It is impossible to completely get rid of friction, but it can be reduced.

20. Using friction  Friction is also important to anyone driving a car.  Grooved tire treads allow space for water to be channeled away from the road-tire contact point, allowing for MORE friction in wet conditions.

21. Using friction  Shoes are designed to increase the friction between their soles and the ground. How do you think these shoes increase friction?

23. Modify your “Sail Car”  Use materials to make modifications to the sail.  Increase your friction by 10% or decrease your friction by 10%