BODIES IN MOTION
WILL REMAIN IN
ACTED UPON BY AN
As long as one of your tires is touching the earth, you
can change your bike’s speed and direction at will. But,
once it takes flight, you may as well be a large rock. You
can cheat the wind, but you can’t cheat physics.
If you paid attention in school, you will remember Isaac
Newton’s little ditty, “Bodies in motion will remain in
motion unless acted upon by an outside force.” The outside
forces on a flying motorcycle are gravity, which accelerates
you back to earth, and wind resistance, which slows you
down while you are up there.
When you jump your bike, barring a strong crosswind,
the speed, angle and force with which you hit the ramp
establish an arc that will take you in an otherwise straight
line to a predetermined point. Hopefully, that point will be
somewhere on the racecourse.
SIR ISAAC’S SCHOOL
Isaac Newton had another catchy tune. It went, “For
every action there is an equal and opposite reaction.” In
this case, the energy stored in the mass of the motorcycle’s
spinning rear wheel is the key player.
Because you and your motorcycle were launched at the
same speed, in the same arc, the two of you fall to earth at
the same rate. And, until you smack back to the ground, for
all practical purposes you are weightless bodies in space.
But, this assumes that your rear wheel is spinning at the
exact same rpm as it was when it left the ramp, which
is rare. If the rear wheel spins faster or slower, the game
of flight takes on some new possibilities. There is a lot of
energy stored in the mass of the spinning wheel.
WHAT HAPPENS IF THE REAR
WHEEL SLOWS DOWN?
You can transfer the stored energy of the spinning wheel
to your bike’s frame by tapping the rear brake. Touching
the brake stops the rear wheel from spinning (that’s the
“action” part of Newton’s equation), and this action causes
a reaction to the part of the motorcycle attached to the
rear wheel (the frame). If the wheel, which was spinning
counterclockwise stops—or, in essence, sends its forces
backwards in a clockwise motion—the frame of the motorcycle will react in the opposite counterclockwise direction.