The Harder You Hit The Brakes While Driving Forward,the More The Rear End Will Move Up(the Front End Move Down).Why?


2 Answers

Oddman Profile
Oddman answered
Consider where the center of mass of the car is relative to where the force is being applied. The force is a rearward force applied to the tires at the pavement surface. The center of mass of the car is a couple of feet off the pavement. Thus, there is a torque around the center of mass that causes the rear of the car to rise and the front to fall. The suspension allows this motion to take place. The faster you stop, the greater the force, the greater the torque.

Presumably, a "smart" suspension could compensate for the horizontal acceleration, so the car could be stopped without that dip in the hood. (As a motorcycle rider, I was taught to look for that dip in the hood to tell whether a car was slowing or not. Such a suspension could give false clues.)
thanked the writer.
Vin Ravun
Vin Ravun commented
Thank you! Isn't the torque due to friction?
Oddman commented
Yes, it is. A car does not stop, go, or steer without friction against the roadway.
Chris m Profile
Chris m answered
Probably bad struts in the front
thanked the writer.
Vin Ravun
Vin Ravun commented
Thank you but What's the physics behind it?
Chris m
Chris m commented
As the front struts are a spring and shock assembly, with the front strut shocks being shot they will not create any resistance. As the momentum of the car transfers forward during braking. Thus as the nose dives down it will allow more momentum to transfer more weight to the front and less to the rear. Have someone sit on the front right fender and watch how high the left rear corner lifts!

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