1. RACE CARS (Compressed Air Cars)
8th Grade Ind. Tech
Miss Check

2. Table of Contents Unit 1- Understand the Problem
Unit 2- Gather Information
Unit 3-Develop Solutions
Unit 4-Implement a Solution
Unit 5-Test and Evaluate
Unit 6-Redesign and Communicate

3. Unit 4 – Implement A Solution
In this activity you will:
--Learn about friction.
-Implement a solution for the CO2 Car Design project.
-Cut out, shape, and finish your car.
-Keep safety in mind while building your car.

4. Skin Friction Glossary
Friction- When two surfaces rub together, the irregularities of the surfaces catch again each other. Friction is the force one surface exerts on the other when they rub together.
Skin Friction- Skin friction is friction that takes place in a thin layer of air surrounding the surface of an object. Skin friction is caused by the collision of particles between the object and the air.
** The rougher the surface of the object, the greater the skin friction.

5. Skin Friction- Yellow Car
This car has a standard body design and is made from light materials. Because the car has not been sanded, the finish is very rough.

6. Skin Friction- Blue Car
This car has a standard body design and is made from light materials. The car has been sanded a small amount. Some areas that are smooth, while others are still rough to the touch.

7. Skin Friction- Red Car
This car has a standard body design and is made from light materials. The car is very smooth and well-sanded. There are no rough areas.

8. Summary
Friction is the force one surface exerts on the other when they rub together. It is a type of drag.
Skin friction is a friction that is caused by the collision of particles between the object and the air.
To reduce skin friction, sand the car until it is smooth.

9. Rolling Friction Glossary
Friction- Recall that friction is the force one surface exerts on the other when they rub together.
Rolling Friction- Rolling friction occurs when an object rolls over a surface. The most common place where rolling friction occurs on a race car is between the axles and the body.

10. Yellow Car
This car has standard body design and is made from light materials. The axle is perpendicular, or at a 90 degree angle to the car body. The axle has been lubricated, or oiled.
90 degrees
Race Time – seconds

11. Blue Car
This car has a standard body design and is made from light materials. The axle is not perpendicular, or at a 90 degree angle, to the car body. The axle has been lubricated, or oiled.
Race Time seconds

12. Red Car
This car has a standard body design and is made from light materials. The axle is perpendicular, or at a 90 angle, to the car body. The axle has not been lubricated, or oiled.
90 degrees
Race Time – seconds

13. Summary
Rolling friction is the friction that occurs when an object rolls over a surface.
To reduce axle rolling friction, make sure the axles are free from burrs or scratches, are perpendicular to the car body, and are lubricated.

14. Build The Prototype
In this activity, you will build your prototype car. Building a prototype involves several steps.
1. The first step is to prepare to cut the car.
a. Use scissors to cut out the car views from your Design Sketch.
b. Use a marker to trace the cut-outs onto the car body.
c. And then mark the axle holes.
2. Next, create axle holes on the car body. Axle holes must be exactly parallel, or even, with the bottom of the car body.
3. Then, cut out your car. You will use the scroll saw to do so.
4. It is a good idea to make sure your car meets the Race Car Specifications before continuing.

15. Finish the Car The next step is to shape the car.
Then reduce skin friction. You can reduce skin friction on your car by sanding the car until it is smooth.
Then you assemble the car. Assembling the car involves installing the wheels and axles correctly. It involves making sure the wheels and axles have good rolling friction.
4. After the car is finished, roll it gentry across a table or flat surface to check if the wheels roll smoothly but are not loose.