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 Work, Power and Kinetic energy

Let us do some work!

Work done (J) = Force (N) x Distance moved (m)

If you move a 1 Newton iPhone for 1 metre, you have just done 1Joule of work.

In terms of electricity:

Work (J) = Charge (Coulomb) x Voltage (volts)

It is similar to the above because Voltage (potential difference) moves the charge along the conductor.

Important points to remember when calculating work done:

  • Always make sure cm, mm are changed to metres
  • Grams and kilograms must be changed to Newtons (100g = 1N, 1kg = 10N)

Gravitational field strength

A mass of 1kg is pulled down by a gravitational force of 10N on earth. This is the gravitational field strength i.e. 10N/kg

So if your mass is 70kg, every kilo in you is being pulled down by a force of 10N.

Gravitational Potential Energy (GPE)

A raised object stores energy as Gravitational Potential Energy (GPE).

We can use the relationship above to find out how much GPE an object has:

GPE (J) = mass (kg) x gravitational field strength (N/Kg)x Height (m)

Kinetic Energy

*Remember, energy cannot be created nor destroyed but it can be transferred.

So, when the object drops, the GPE is changed into Kinetic energy.

We can calculate kinetic energy using the equation below:

Kinetic energy (J) = 1/2 xmass (kg) x velocity2

Terminal velocity

As an object falls, more and more GPE is transfered into Kinetic energy (KE), meaning that the object will continue to accelerate downwards.

But there will come a point where drag (air resistance) equals the downward force of gravity. At this point, the object will be travelling at terminal velocity. The object will fall at a constant speed.

Parachutes increase drag, so the object reaches terminal velocity quicker before it reaches a very high free fall speed. At this point, it will fall at a steady, safe speed.