POWER MY CAR
Learning Intention:
To understand how sails help objects move. To understand what kinetic energy is. To use this knowledge and problem solving skills to create a sail car.
Sailing on land? Thanks to Dave on Arrival for the video
Discussion:
Why do you think sailors love the wind? How can wind help them? Sailboats harness the power of the wind. What does that mean?
Sailors rely on wind to get where they are going. Wind transports them from one place to another. When wind pushes on a sail it exerts an energy force on the sail and this force pushes the boat forward.
What is the type of energy that moving objects have?
It is called kinetic energy. Anything that is moving has kinetic energy.
We are going to look at the energy used to power a sail car. Have you seen or heard of land yachts or blokarts? They function like a sailboat, but on land, still using a sail to power them, but have three or four wheels and are steered by pedals or hand levers. The sail car you will make will have a sail and wheels like a land yacht.
Land yachts or Blokarts can travel very fast. Some go 100 km/hr. Ice yachts are land yachts that sail on ice or snow. But, instead of rolling on wheels, they glide on runners.
For your sail cars to move forward the force must be big enough to overcome any friction in the spinning axles. That friction can be greater if your axles are misaligned or if your wheels are wobbly.
Will a bigger sail make the sail car go faster? Will the shape of the sail matter?
Activity: Build a sail car and test it.
Materials:
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Corrugated cardboard (recycled box)
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Construction paper or card
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Three wooden skewers
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Two straws - preferably paper
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Four plastic bottle caps (use card or recycled plastic circles if you don't have a supply of caps)
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Craft knife
Procedure:
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Cut out a piece of cardboard for the body of your car. Tape two straws across the bottom of your car, one at each end. Make sure the straws are parallel.
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Have an adult use the craft knife to carefully poke a "+" shaped hole in the center of each bottle cap. Or heat the end of a metal skewer or pointy scissors with a lighter or candle and poke a hole in the caps.
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Push a wooden skewer through the hole in one of the bottle caps
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Thread the other end of the skewer through one of the straws.
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Push a bottle cap onto the end of the skewer opposite the first bottle cap. You just made an axle with two wheels for your car!
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Repeat these steps to make the other axle.
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Make sure the axles can spin and the car can roll smoothly without getting stuck. If needed, adjust the wheels so they are not too wobbly. You can put a dab of hot glue on the outside of the wheel, to the skewer.
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Have an adult use the craft knife to carefully poke a small hole in the middle of the cardboard. Or use a drawing pin to poke a hole.
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Insert a wooden skewer upright into the hole to form a mast for your car's sail. Secure it at the base with plenty of tape or hot glue. If it is still too wobbly, you can build a diagonal support out of a piece of cardboard.
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Make at least three sails that are all the same shape but different sizes.
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Poke the upright skewer through both ends of your smallest sail to hold it in place.
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Decorate your sail car if you wish.
Testing:
Make a prediction. How will your car go with the smaller sail compared to the larger one?
Place your fan on the floor at one end of a long corridor or large room.
Place your car in front of the fan. How far does your car go before it stops?
You may want to use a stopwatch to time it. Or measure the distance the car traveled. To calculate the speed of the car, divide distance by time. Conduct three trials and then calculate the car’s average distance, time, and speed.
Replace the smallest sail with your next-biggest sail, and try again. How far does your car go this time?
Try with your largest sail. Does the car go as far as you expected?
Take the car outside and try it in the wind. What will happen?
Race your car with others. Whose will be the fastest? Why do you think that?
Record all of your findings.
Extra:
Did you notice with a small sail, that your sail car started out very slowly. The wind exerts only a small force on the small sail, so it may be difficult to overcome friction in the axles to get the car moving. The car will start moving more quickly and go farther with a larger sail. There can be disadvantages of a larger sail. Eventually the extra wind the sail can catch doesn’t make up for the extra weight of the sail, so continuing to make the sail bigger will not make the car travel any farther.
Experiment with your car to make it go faster. Try sails that are different shapes. What shape works the best?
Try changing different parts of the car. What can you change to make it go faster or farther? The base shape or size or a taller mast. Change some of the materials you used. For example: Plastic or fabric for the sail or different wheels. Can you make the sail car with three wheels?
Glossary:
Wind energy, pungao hau - Electrical energy sourced from harnessing the wind with windmills or wind turbines.
Renewable energy - Energy from something that is not depleted when it is used, like wind or solar power.
Windmill, purere kapo hau - A structure that converts wind power to pump water or mill grain.
Wind turbine, Kopohau - Tall towers with blades that turn in the wind to generate electricity.
Wind farm - A large group of wind turbines for electricity supply.
Lift (in sailing) - An upward force on an aircraft wing or aerofoil. Lift is the result of pressure differences between the top and bottom of an aerofoil.
Drag - The resistance to the movement of a boat through water.
Kinetic energy - The energy of anything moving such as a boat moving or a ball when kicked.
Friction - Is the resistance of motion when an object rubs against another object.
Axle - A rod passing through the centre of a wheel.