So what is kinetic energy? There's motion everywhere in our world. What if we could harness the energy that would otherwise be wasted to power our gadgets and generate clean electricity? Is it too good to be true? We've written many articles about various things that do that, from small gadgets to big infrastructure, but we've never really looked at the field as a whole, with an explanation of how it works and an overview of the pros and cons of trying to harness kinetic energy.

Kinetic Energy Explained



So first thing first: Kinetic energy is the energy of motion. Accelerating an object from a rest position to a certain velocity takes energy, and the object maintains that energy as long as its speed doesn't change. When the object decelerates, that energy from its motion can be transferred in various ways.

If we're talking about a brake pad on a bicycle wheel, the movement of the wheels is progressively stopped using friction, and the kinetic energy is transformed into heat, which in this case doesn't do anything useful. But there are ways to harness kinetic energy to either generate useful mechanical work or electricity. This is what many have tried to do to make use of energy that would be otherwise wasted.

Methods to Harness Kinetic Energy



One way to harness kinetic energy that has popped up many times in recent years has to do with roads and speed bumps. The latter makes sense because you want vehicles to slow down when they pass over speed bumps, but otherwise, if it's just on a regular part of the road, it's literally highway robbery.

© Courtesy of New Energy Technologies Inc.

Shown above is one of the speed bump kinetic generators.

Olympic Delivery Authority/via

The kinetic sidewalk above was installed for the 2012 London Olympics.

© Empower Playgrounds

Now that's a clever one! This merry-go-round produces electricity from kids playing with it. It was installed in Ghana, where access to electricity isn't always simple.

What is the problem with trying to harness kinetic energy?

While the concept of harnessing mechanical energy that would otherwise be wasted to do useful work is very attractive in theory, in practice, we're faced with big challenges. The biggest is that in physics, there's no such thing as a free lunch. If you get energy, you are getting it from somewhere. So if you generate electricity by having a car drive over something, you are slowing down that car compared to a perfectly flat and solid road, and so this means the engine has to work a little bit harder.

So unless you either only need so little energy that the energy source won't notice the difference, like a self-winding/automatic watch (shown below), or if you can somehow only activate the kinetic system when you would want to take energy out of the system anyway, like with speed bumps (when you want people to slow down) and regenerative braking on hybrids, electric cars and some trains, you are probably better using the money that you'd spend on the kinetic energy-harnessing device and spending it on solar panels. They're likely to produce many more kWh of energy over time than even a well-positioned kinetic generator...

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