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# Mass Or Weight Driven Car

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I’m posting this again as the other thread is really old and I have more questions about how to build one. This is a project for a high school physics class. Here’s the general instructiona:

Edited by Oranjwoman
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I’m posting this again as the other thread is really old and I have more questions about how to build one. This is a project for a high school physics class. Here’s the general instructiona:

I'm not clear what the setup is. How does the falling mass transfer a force to accelerate the car? You mention a string attached to an axle. How does the mass fall, over what distance does it drop and how is it attached to the string?  Are you using anything to multiply the length of time for which the mass pulls the car, i.e. less force but pulling the string for longer, e.g pulley or gears etc?

Edited by exchemist
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Oranji-woman

Your basic problem with using gravity as a power source is always going to remain the same: it degrades by friction or the gravity is so strong as to take over.

Also, think of a hydroelectric scheme: there, other energy sources drive the conditions to a gravitationally useful state.

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To exchemist

“I'm not clear what the setup is. How does the falling mass transfer a force to accelerate the car? You mention a string attached to an axle. How does the mass fall, over what distance does it drop and how is it attached to the string? Are you using anything to multiply the length of time for which the mass pulls the car, i.e. less force but pulling the string for longer, e.g pulley or gears etc? ”

The mass is connected to one end of the string. The other end of string is connected to a small pin that is nailed into the wooden rear (dowel) axle. It is then wound tightly around the rear axel of the car, pulled up and over a wooden dowel which is 3 feet from the bottom of the car. When the weight starts to fall, the attached string rotates the axle, moving the car forward. There are videos on YouTube if you’ve not seen what it looks like. No pulleys or gears on mine as my research showed it would not really help, but just add weight to the car which would cause more resistance and slow the car more quickly.

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• 2 weeks later...

To exchemist

“I'm not clear what the setup is. How does the falling mass transfer a force to accelerate the car? You mention a string attached to an axle. How does the mass fall, over what distance does it drop and how is it attached to the string? Are you using anything to multiply the length of time for which the mass pulls the car, i.e. less force but pulling the string for longer, e.g pulley or gears etc? ”

The mass is connected to one end of the string. The other end of string is connected to a small pin that is nailed into the wooden rear (dowel) axle. It is then wound tightly around the rear axel of the car, pulled up and over a wooden dowel which is 3 feet from the bottom of the car. When the weight starts to fall, the attached string rotates the axle, moving the car forward. There are videos on YouTube if you’ve not seen what it looks like. No pulleys or gears on mine as my research showed it would not really help, but just add weight to the car which would cause more resistance and slow the car more quickly.

I would try putting a thicker section on the rear axle for the string to wind around. This 'drum' will increase the torque (I think I said that right) and the car will accelerate faster. Think low gear in a car. In the other thread I speculated on making this thicker section cone shaped, so the weight string starts wrapping on the thickest (largest diameter) section and then works the winding down to smaller diameter. Think automatic transmission.  Hope this is more helpful than not and timely enough as I have been away.

Edited by Turtle
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• 3 weeks later...

To exchemist

“I'm not clear what the setup is. How does the falling mass transfer a force to accelerate the car? You mention a string attached to an axle. How does the mass fall, over what distance does it drop and how is it attached to the string? Are you using anything to multiply the length of time for which the mass pulls the car, i.e. less force but pulling the string for longer, e.g pulley or gears etc? ”

The mass is connected to one end of the string. The other end of string is connected to a small pin that is nailed into the wooden rear (dowel) axle. It is then wound tightly around the rear axel of the car, pulled up and over a wooden dowel which is 3 feet from the bottom of the car. When the weight starts to fall, the attached string rotates the axle, moving the car forward. There are videos on YouTube if you’ve not seen what it looks like. No pulleys or gears on mine as my research showed it would not really help, but just add weight to the car which would cause more resistance and slow the car more quickly.

I get the impression from this that because the string is pinned to the axle it is stopping when all the string is wound off and tight.

Is that what is happening?

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