Energy Types and Calculations
Kinetic energy is what every moving object possesses, whether it's a car speeding down the motorway or a tennis ball flying through the air. The faster something moves or the heavier it is, the more kinetic energy it has.
You can calculate kinetic energy using KE = ½mv². This means kinetic energy equals half the mass times the speed squared. Notice how speed is squared - this means doubling the speed actually gives four times more energy, which is why car crashes are so much more dangerous at higher speeds.
Gravitational potential energy is stored energy that objects have when they're above ground level. A book on a high shelf has more gravitational potential energy than one on a lower shelf. The formula GPE = mgh shows this depends on mass, gravity (10 N/kg on Earth), and height.
Elastic potential energy gets stored when you stretch or compress something like a spring or rubber band. The more you stretch it, the more energy it stores, following the formula EPE = ½kx². The spring constant tells you how stiff the spring is.
Quick Tip: Remember that energy can't be created or destroyed - it just changes from one type to another, like when a bouncing ball converts between kinetic and gravitational potential energy.
When objects fall or rise, energy converts between kinetic and gravitational potential energy. Using ½mv² = mgh, you can work out how fast something will be moving when it hits the ground or how high it will go.
Work done measures energy transfer (force × distance), whilst power measures how quickly energy is used or transferred. Power equals work done divided by time, measured in watts - the same unit on your light bulbs and phone chargers.