Forces - 5.1.1 Scalar and Vector Quantities (GCSE Physics AQA)

Scalar and Vector Quantities

Scalar Quantities

• Scalar quantities have magnitude only. Some things, like speed and temperature, can only be measured by magnitude (size). For example, speed tells how fast the object is moving, but no other information.

Vector Quantities

• Vector quantities have magnitude and associated direction. Some things, like forces and velocity, can be measured by magnitude and direction. For example, velocity tells us the speed and direction of travel.
• We need to know 6 main vectors for AQA exams. These are weight, force, momentum, acceleration, displacement and velocity.

Drawing Vector Diagrams

We can draw vectors in diagrams using arrows. The arrow has both:

• Size – the length of the arrow is related to the size of the vector. If there is a scale on the side saying that 1cm = 5m, then a 4cm vector line would be equal to 20m.
• Direction – if it’s a vector, don’t forget about direction. The direction of the arrow is very important. For example, you might have two arrows which are equal in length, but point in opposite directions, as in Fig 3.