- Define friction
- Describe the relationship between friction and speed
- Describe the relationship between friction and race car safety
- The Force of Friction Activity Sheet
- Toy car or completed car from Unit 1: Aerodynamics
- Tape measures or rulers
- Various surfaces (such as tinfoil, fine sandpaper, rough sandpaper, wax paper, carpet)
- Make copies of the activity sheet for each student in your class.
Think: How are kinetic energy and friction related?
- Ask students to define friction—the resistance that one surface experiences when moving over another. For example, as a spinning tire rolls over a racetrack, the tire’s surface catches against the road, creating friction that improves traction and helps race cars gain speed and increase grip. Grip, which is another word for friction, helps race cars stay on the track, even when navigating turns at high speeds.
- At NASCAR, car tires, the race car’s aerodynamics, and the surface of the roads are all fine-tuned to ensure the race cars make solid contact with the ground. NASCAR tires are smoother than the tires on everyday vehicles. This allows more surface area on the tire to be in contact with the track. This smooth surface area provides greater grip at higher speeds, keeping race cars safe on the track. In addition, NASCAR tracks are made of specific surfaces, such as asphalt or concrete, which help tire friction and performance. Rougher surfaces increase friction, while smoother surfaces allow objects to slide more easily over them.
- While friction can increase safety in race cars, it can cause problems, too. Due to a race car’s high speed, there is a lot of friction where the tires rub against the road. The friction takes some of the race car’s kinetic energy and converts it into heat energy. As a result, the race car’s tires become very hot and can eventually fall apart. This is why race car teams change tires multiple times during a race.
Move: What type of energy is created by friction?
Step 1: Demonstrate how friction is heat energy by having students rub their hands together. Point out that the more vigorously they rub them, the warmer their hands will become. Any two surfaces that rub together will create heat.
Step 2: Point out that friction depends on a force pushing two surfaces together. For example, when you rub your hands together, the more force you apply, the more friction and heat you will create. If there is no force, there is no contact; therefore, there is no friction.
Build: What types of surfaces create the most friction?
Step 1: Distribute The Force of Friction Activity Sheet and tell students that they will build a high-friction racetrack to demonstrate the effects of friction on a rolling car. Point out that any contact between atoms or molecules that are moving against each other will create friction. Rough surfaces have more matter exposed than smooth surfaces— more nooks and crannies—and this can create more available spots for possible friction.
Step 2: After the discussion, have students create a cause-and-effect chart that analyzes the impact of friction on their experiment and have them explain the effects of friction on kinetic energy.
Team Up: How can we diminish friction?
Step 1: Explain that race car engineers study friction to improve the speed of race cars. They work to diminish friction so the cars can move quickly, but they don’t want to get rid of friction altogether, because friction allows the cars to slow down and stop.
Step 2: Divide students into problem-solving teams and give them the task of brainstorming ways to remove friction from their daily lives. Their lists should include sources of friction around them and an explanation of how removing that friction would make their lives better. If they need idea prompts, share this list of everyday items that experience friction: car tires, skateboard wheels, train tracks, revolving doors, zippers. Have groups present their recommendations to the class.