To maximize its chance of escape, a grasshopper needs to jump a long way, and to do so quickly. So a good jump needs two things:
First, the legs have to thrust on the ground with a lot
of force.
If the force is too low, the animal doesn't get a fast
enough take-off and it doesn't jump very far (or maybe doesn't get off the ground at all).
Second, the legs have to apply this force quickly.
If the force builds up too slowly, the legs will fully extend
before the thrust reaches its maximum. Once the
grasshopper is standing on tip-toe, it can't push
against the ground any more.
Science
stuff: equations of motion and some facts and figures.
A failed jump: the thrust is too slow or too weak. Note that there is no delay between the initial flexion and the attempted jump. (Again, the cartoon is just for illustration
- it is not a tracing from a real grasshopper.)
So remember, a good jump means that the legs must push against
the ground with high force, and high speed.
To be precise (or reasonably so), a typical grasshopper weighing
2-3 gm will thrust against the ground with a force which peaks at about 30 gms
when the legs are half extended, to give it a final take-off velocity of about
3 m.s-1.
The ultimate source of this push comes from the contraction of
the muscles inside the leg, so let's start off by seeing how the muscles make
the leg move...