Have you ever wanted to impress your friends with a cool physics project? Well you're in luck!!
My instructable will teach you how to build the simplest kind of heat engine. This instructable is a cheap (roughly $20 cost) and a simple idea to build for a basic physics demonstration. The total time to build takes only an hour from start to finish. The importance of this project stresses the simplicity of demonstrating a simple heat engine through heat energy converted into mechanical motion.
Building this rubber band heat engine is one of the simplest and coolest ways to demonstrate how work is done through the use of heat. You can also impress your friends by telling them you're building an "engine".
What is a heat engine?
A heat engine is a machine that converts heat energy into mechanical motion. The Rubberband engine will convert heat engery, using a heat lamp, into a mechanical motion by spinning the wheel.
How does this work?
Rubber bands react opposite of metals when exposed to hot and cold temperatures. When exposed to a (hot) heat lamp, the rubber bands will contract and become smaller. As they contract, the center axle will shift towards the outer rim of the wheel causing the wheel to become unbalanced. When the wheel is unbalanced, it will cause the weight to shift and begin to spin! Henceforth, heat energy has now been converted into mechanical motion.
Follow the next 6 steps carefully and you will soon have a fully functional rubber band heat engine!
NOTE: Building this heat engine is a bit challenging for children but could easily be accompanied by someone of the age 12+.
Step 1: Gather the Materials
- Fully functional bike rim (no tire or rubber tube)
The bike rim should be in good shape. Don't use a bent up old rim.- Small bolt cutters
Pliers will not cut through the aluminum spokes. You will need a sharp and sturdy pair of small bolt cutters.- Heat lamp bulb
You may use a regular heat lamp from any hardware store or you can purchase just the bulb and use a standard desk lamp as the source to put the bulb.- 3inch Rubberbands.
Rubber bands react the same to heat no matter what size, shape, or width. However, for the best result, I recommend 3 inch rubber bands that are a little thicker and stronger to hold the wheel and axle together.
After you have these materials gathered, you are now ready to begin building your rubber band heat engine.
Step 2: Marking the Spokes
1. Measure the length of one spoke.
My bike wheel is 26 inches in diameter. Therefore each spoke has a length of 11.5 inches.2. Mark 1.75 inches off the tip of the spoke near the axle.
3. Mark 1.75 inches off the tip of the small aluminum stud.
4. Repeat sub-steps 2 and 3 so that every spoke is marked the same around the wheel.
Tip: If you don't have a 26 inch diameter bike wheel, no worries. You can still mark 1.75 inches off each end of the spoke because it gives you the best room for the next step, cutting and bending the hooks.
Step 3: Cutting & Bending Hooks
Using bolt cutters can be a pinch point and will need to be used with caution when cutting.
Aluminum is sharp when cut. Use caution and to not poke yourself when bending hooks.
1. Cut only ONE spoke at the marks you made in step 2.
2. Remove the small aluminum piece near the axle
3. Bend a hook on the small piece of axle you have just removed.
CAUTION! Bending the aluminum piece too much can cause it to break.
Tip: Hold the piece tightly in the pliers and press against a hard surface to make it a little easier to bend.
4. Replace the bent aluminum piece back into the axle.
5. Bend a hook into the small aluminum piece of the rim with pliers or bolt cutters to have a hook at the "cut" end.
Step 4: Replacing and Repeating
Stretching rubber band to far could cause it to snap and leave a welt on your hand. Stretch with caution.
1. Stretch a rubber band over the two hooks you have made in step 3.
You are now replacing the spoke with a rubber band.2. Repeat step 3-4.
Tip: Cut only one spoke at a time replacing it with the rubber band. This helps so that you don't lose track when remembering the configuration of the spokes of a bike rim. It also keeps the wheel balanced
Step 5: Setting Up Rubber Band Heat Engine
Outcome: The wheel should spin freely without rolling of the platform. You may use the bolt already in the axle of the wheel, or since mine doesn't have one, I used a wooden rod allow the wheel to spin.
Heat lamps become very hot when in use. Use caution not to burn your skin on the bulb.
2. Stand the heat lamp 6 inches away from the rubber bands, level with the axle.
Tip: Position the lamp closer to the rim to get a better spin on the wheel.
Step 6: Complete Rubber Band Heat Engine
1. Turn on heat lamp.
2. Wait 5 minutes for the lamp to become hot and for the rubber bands to begin contracting
3. Watch carefully as the wheel spins!
You now have successfully built your first rubber band heat engine!!!
Click HERE to watch the video of the wheel spinning.
The wheel will spin as the rubber bands continue to stretch, due to the heat, and shift the center axle.
You will notice that the wheel spins quickly in one direction, and then reverses in the other. This is because the axle is shifting towards one side of the rim, causing it to become unbalanced. The wheel will continue to rotate back and forth until a new set of rubber bands are heated up to continue rotating the wheel.
Note: This heat engine cannot be used to perform much work. However, the design is very unique and cool to watch as the bands stretch and the wheel continues to spin.