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Old 01-08-2020, 08:32 PM   #29 (permalink)
LioNiNoiL
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Quote:
Originally Posted by EcoCivic View Post
I can't think of a good way to measure brake drag other than how long the wheel spins
That is actually a definitive method - the torque from brake+bearing* drag is (very nearly) constant, so the rate of decrease of wheel rotational velocity is constant, therefore that velocity decreases linearly (to zero) with time. The result is the ratio of times to stop (assuming the same initial velocity) is the inverse ratio of total drag.
Quote:
about 5-10 seconds with the disc brakes... Now it will spin for around 15 seconds
...so two to three times as much, therefore one-third to one-half the drag.
Question 3 of the 2018 AP Physics test is a good reference to this phenomenon.

*air resistance at low speed is negligible.

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