What causes the back of a bike to lift when the front brake is applied? (Like in an endo.)
Also, if I were to replicate this effect with a wood block with wheels that crashes against a wall (only the wheels touch the wall) would it work?
Answer
If we disregard wind resistance, there are three points where external forces apply to the combined bike/rider body: The front and rear wheel contact points with the road, and the combined center of mass. If these forces generate a torque that is not zero, the rear wheel will lift off while braking (or the front wheel lift off during hard acceleration).
If you want to replicate the system with a block of wood with wheels bumping into a wall, use very small wheels. If the front wheel suddenly stops due to braking on a bike, the bike will rotate around the contact point of the front wheel. On the other side, if you run the front wheel into a wall, the front wheel will stop and the center of the rotation will be the front wheel hub. (Assuming sufficiently stiff wheels.)
Some time ago, I have hacked together an interactive web page showing the forces to a braking/accelerating trike/bike on different slopes. Playing with that page might help you understand (requires SVG+CSS+Javascript).
I have originally built the page for a tadpole tricycle. For looking at a standard bicycle, select "upright bicycle" on the page and then play a little with the + and - buttons for the acceleration/deceleration. If you have understood what is going on, try the + and - buttons for the slope as well.
No comments:
Post a Comment