Re: why do locusts have more power when they jump than humans?

Caroline,

It is actually quite possible for something as small as a locust to expend 
more power than a human being, and I can think of two ways this could be 
so. To explain, we'll have to consider the difference between energy (or 
work) and power.

Energy is a measure of the ability to perform some kind of work. It's 
defined in units called joules, defined as a newton-meter (or, more 
basically, as a kilogram(meter/second)^2. Looking at this, it means that 
moving a one-kilogram object one meter by applying a one-newton force 
would expend one joule of energy.

Looking at a human about my size, they would mass about 75 kilograms and 
have a weight of 735 newtons. If that person jumped one meter off the 
ground they would expend 735 newtons x 1 meter = 735 joules of energy.

A locust masses around twenty grams or so (.o2 kilograms) and weighs 
about .2 newtons. If the locust were to jump one meter off the ground it 
would expend .2 newtons x 1 meter = .2 joules of energy.

So the human definitely needs a lot more energy to move around - in fact, 
almost 3500 times as much!

Power, though, is a little different from energy and is defined as the 
rate at which energy is used. The unit of power is the watt, and one watt 
of power is defined as one joule of energy released per second. 

Looking at our person who just jumped a meter off the ground, we can 
determine what power was expended to get up into the air. Let's say that 
when he jumped, his legs worked for about a second to push him into the 
air and he coasted to one meter once he left the ground. All 735 joules of 
energy were expended in that second. The power in watts expended is then 
735 joules / one second = 735 watts.

The ant, though, moves much faster than the human being: its jumping 
action is measured in thousandths of a second. Assuming the time it's 
touching the ground is one-thousandth of a second, then the power expended 
is .2 joules / .oo1 second = 200 watts. We haven't quite reached the power 
used to move the human, but it's not very far off, either - especially 
impressive since the locust is so much smaller than a person!

What's really impressive, though, is a value called specific power. 
This is defined as the power expended by a source divided by the weight of 
that source. It's a way of measuring how much power per unit weight can be 
supplied.

For the human being, the power was 735 watts. Dividing by the human's 
weight - 735 Newtons - we get a specific power of 735 watts / 735 newtons 
= 1 watt per newton. Not a very big number.

For the locust, the specific power is 200 watts / .2 newtons = 1000 watts 
per newton. This means that a locust releases more a thousand times more 
energy per newton of weight than a human does - if a human had the same 
specific power, he would jump a thousand meters!

I hope this has been helpful!