Wheel Diameter?

• Call4ljw

  1 Aug 11, 07:40

  Not really a homework, just curiosity.

   

  But anyway, which gives a higher speed, larger or smaller wheel?

   

  regards.

• wee_ws

  1 Aug 11, 07:55

  Hi,

    The rate at which a wheel revolves would matter more. Thanks.

  Cheers,
  Wen Shih

• Call4ljw

  1 Aug 11, 08:59

  Originally posted by wee_ws:

  Hi,

    The rate at which a wheel revolves would matter more. Thanks.

  Cheers,
  Wen Shih

  So lets say that for both situations, the motor is of the same power / rpm, which wheel size will have a higher speed?

  Thanks.

• lce

  1 Aug 11, 10:05

  rpm is rpm , no faster or slower

  if car, bigger wheels require bigger torque hence higher rpm

• Blacktron

  1 Aug 11, 10:06

  RPM = Rotation per minutes
• eagle

  1 Aug 11, 10:08

  Hi,

  I presume you are talking about the chapter of circular motion in A level physics, or something similar to this.

  In circular motion, ω is the radians per second, or rather, a measure of the rpm in terms of radians. We also have tangential velocity, where v = rω.

  Using the formula v = rω, we can see that the further you are from the radius or rotation, the faster your tangential speed.

  You cannot really say which wheel size has a higher speed, because the speed depends on the distance from the centre of the wheel. You could only probably give a question on which wheel has a faster tangential velocity, which in this case, is the wheel with a larger radius.

• Call4ljw

  1 Aug 11, 16:37

  Originally posted by lce:

  rpm is rpm , no faster or slower

  ??

  I meant rpm of the motor which after gearing is of a different rpm from the wheel.

• Call4ljw

  1 Aug 11, 16:40

  Originally posted by eagle:

  Hi,

  I presume you are talking about the chapter of circular motion in A level physics, or something similar to this.

  In circular motion, ω is the radians per second, or rather, a measure of the rpm in terms of radians. We also have tangential velocity, where v = rω.

  Using the formula v = rω, we can see that the further you are from the radius or rotation, the faster your tangential speed.

  You cannot really say which wheel size has a higher speed, because the speed depends on the distance from the centre of the wheel. You could only probably give a question on which wheel has a faster tangential velocity, which in this case, is the wheel with a larger radius.

  A level? I only up to O level lol.

• Call4ljw

  1 Aug 11, 16:44

  Originally posted by eagle:

  Hi,

  I presume you are talking about the chapter of circular motion in A level physics, or something similar to this.

  In circular motion, ω is the radians per second, or rather, a measure of the rpm in terms of radians. We also have tangential velocity, where v = rω.

  Using the formula v = rω, we can see that the further you are from the radius or rotation, the faster your tangential speed.

  You cannot really say which wheel size has a higher speed, because the speed depends on the distance from the centre of the wheel. You could only probably give a question on which wheel has a faster tangential velocity, which in this case, is the wheel with a larger radius.

  So unlike gears which either give speed or power, larger wheels give both speed and power?

• lce

  1 Aug 11, 16:48

  Originally posted by Call4ljw:

  ??

  I meant rpm of the motor which after gearing is of a different rpm from the wheel.

  
  yes, the transmission(gearbox) / crown & pinion ratio

  but everything has to be matched from powertrain to driveline

• eagle

  1 Aug 11, 17:29

  Originally posted by Call4ljw:

  So unlike gears which either give speed or power, larger wheels give both speed and power?

  Gears and wheels are two different things.

  Gears make use of the principle of moments. Basically, because of conservation of energy, power is the same, but the torque can be higher or lower.

   

   

• Call4ljw

  1 Aug 11, 22:45

  Originally posted by eagle:

  Gears and wheels are two different things.

  Gears make use of the principle of moments. Basically, because of conservation of energy, power is the same, but the torque can be higher or lower.

   

   

  So for example, a car with a larger wheel diameter moves faster and uses less power than a car with a smaller wheel diameter, am I right to say that?

   

  regards.

• gunner77

  1 Aug 11, 23:20

  Originally posted by Blacktron:

  RPM = Rotation per minutes

  
  Revolution per minutes.

• lce

  1 Aug 11, 23:38

  rounds per minute

• ditzy

  1 Aug 11, 23:45

  I can rephrase your question into which bag is heavier, 1kg of solid gold, or 1kg of dried sawdust?

• Call4ljw

  2 Aug 11, 07:21

  Originally posted by ditzy:

  I can rephrase your question into which bag is heavier, 1kg of solid gold, or 1kg of dried sawdust?

  I don't think it works this way, because judging from what I learnt in school so far, larger diamter wheel requires lower power to go the same distance, i'm just not sure about the speed.

  regards.

• eagle

  2 Aug 11, 08:17

  Originally posted by Call4ljw:

  So for example, a car with a larger wheel diameter moves faster and uses less power than a car with a smaller wheel diameter, am I right to say that?

   

  regards.

  wrong. The distance travelled is the same. The total amount of energy used is the same, assuming weight of car, friction, etc, all remain the same.

   

  The definition of power in physics is unlike the layman definition of
  "Wah this car got power to move up the slope leh!"

  In physics, it is
  "This car has sufficient torque to move up the slope"

• Call4ljw

  2 Aug 11, 16:29

  Originally posted by eagle:

  wrong. The distance travelled is the same. The total amount of energy used is the same, assuming weight of car, friction, etc, all remain the same.

  Then time?

   

  regards.