## Forces

Forces

The forces are with us

 Word Pronunciation Meaning air resistance A force that tries to slow things down that are moving through air. It is a type of friction. drag Air resistance and water resistance are both sometimes called drag. force A push or a pull. force meter Piece of equipment containing a spring, used to measure forces. friction A force that tries to slow things down when two things rub against each other. gravity The force of attraction between any two objects. The Earth is very big and so has strong gravity that pulls everything down towards it. magnetism A force that attracts objects made out of iron. newton (N) The unit of force. newton meter Another name for a force meter. speed How fast something is moving. Often measured in metres per second (m/s). static electricity A force which attracts things with extra electrical charges on them. upthrust A force that pushes things up. water resistance A force that tries to slow things down that are moving through water. It is a type of friction.

That floating feeling

 Word Pronunciation Meaning density The amount of mass that 1cm3 of a substance has. Measured in g/cm3. upthrust A force that pushes thing up.

Balancing act/Hooked!/Weighing in

 Word Pronunciation Meaning balanced forces When two forces are the same strength, but working in opposite directions. gram A unit for measuring mass (g). gravity The force of attraction between any two objects. The Earth is very big and so has a large gravity pulling everything down towards it. kilogram A unit for measuring mass (kg). There are 1000 g in 1 kg. mass The amount of matter that something is made of. Measured in grams (g) and kilograms (kg). Your mass does not change if you go into space or to another planet. newton The unit of force (N). stationary Not moving. unbalanced forces When two forces working in opposite directions are not the same strength. weight The amount of force with which gravity pulls something towards the Earth. It is measured in newtons (N).

Friction

 Word Pronunciation Meaning lubricant loo-brick-ant A substance (normally a liquid) used to reduce friction. water resistance A force that tries to slow things down that are moving through water. It is a type of friction.

The need for speed

 Word Pronunciation Meaning braking distance The distance a car travels while the brakes are trying to stop it. distance/time graph A graph that shows how far and how fast something travels during a journey. kilometres per hour (km/h) Units for speed when the distance is measured in kilometres and the time is measured in hours. metres per second (m/s) Units for speed when the distance is measured in metres and the time is measured in seconds. miles per hour (mph) Units for speed when the distance is measured in miles and the time is measured in hours. speed How fast something is moving. Often measured in metres per second (m/s). stopping distance The distance a car moves while it is stopping. The stopping distance is equal to the thinking distance and the braking distance added together. thinking distance The distance a car travels while the driver is deciding to press the brake pedal.

Faster and faster

 Word Pronunciation Meaning accelerate ack-sell-er-ate Change speed. air resistance A force that tries to slow down things that are moving through the air. It is a type of friction. balanced forces When two forces are the same strength, but working in opposite directions. friction A force that tries to slow things down when two things rub against each other. unbalanced forces When two forces working in opposite directions are not the same strength.

Drag act

 Word Pronunciation Meaning drag Another name for air resistance or water resistance. streamlined Giving something a smooth shape to reduce the air resistance or water resistance. water resistance A force that tries to slow down things that are moving through water. It is a type of friction.

Hitting the limit

 Word Pronunciation Meaning distance–time graph A graph that shows how far something has moved in a certain time. terminal velocity The maximum speed of an object. Usually only applies to falling objects when the downward force is balanced by drag.