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Given we’ve got the equation, we can see lots of things. In a car, if you want to play first away from the traffic lights (which is getting better acceleration) you can do two things. You can give it a bigger push, with a larger engine. Otherwise you can reduce the mass, make it out of lightweight materials. Of course, a bigger engine is often heavier, so you get more force, but more mass. This is even more crucial in things like aircraft, where you’re wanting to counteract the force of gravity too.
Now this REALLY comes into its own when you consider a rocket. Its true for most powered things, but even more so for rockets. Most of a rockets weight is its fuel. However as the rocket launches it burns up its fuel. So assuming the engines generate a constant thrust (force) things are going to change.
Lets assume the rocket is generating 1 newton of thrust, and weighs one kg. We can work out how fast it will accelerate F=m*a 1=1*a solve for a - well it has to be 1. So this rocket will accelerate at 1 m/s/s. However, a short time later, it may have burnt ½ a kilogram of fuel. So now the rocket weight ½ a kg. So now it’s 1=½*a solve for a - its now 2 m/s/s. When it’s burned ¾ of a kilogram of fuel, its now 1=¼ *a
ICY SCIENCE | QTR 1 2014