ENERGY ENERGY CALCULATIONS - -Work and energy

Weight & Mass Before we look at calculations relating to WORK and ENERGY we have to understand something: Weight and Mass are two different things. 100 kg 100 kg

Weight & Mass continued An objects weight is how hard gravity is pulling on it. We think the weight is the same everywhere... because we all live on the surface of the planet Earth! But if the object were far out in space it would just float around, exerting no force on the scales. The scales would show 0 kg... but the mass is still 100 kg An object's mass doesn't change (unless you remove some!), but its weight can change. 100 kg 100 kg

Weight (Force) & Mass 100 kg 100 kg Weight is a FORCE. The correct unit for force is the Newton, which is abbreviated N. Gravity makes a 1 kilogram mass exert about 9.81 Newtons of force. So a 100kg mass really weighs about 981 Newtons on Earth.

Work and Energy Energy is the ability to do work. Objects that have greater energy can do more work. A force of 20 N pushing an object 5m in the direction of the force does 100 joules of work or 100 Nm. Work (W) is done whenever one form of energy is changed into another form of energy. For example an electric motor does work by changing electrical energy into kinetic energy. To do 100 joules of work, you must expend 100 joules of energy.

Work and Energy Summary Mass is how much matter something has. Mass is anything you can touch physically. Mass is measured in kilograms (Kg). Weight is the affect of gravity acting on a mass. It is a force measured in Newton’s (N). Energy is the ability to do work. Objects that have greater energy can do more work. Work (W) is done whenever one form of energy is changed into another form of energy. Work Done (Nm) = Force (N) x Distance (m) 1Nm = 1 Joule – copy this into your notes