Measurement and Motion: notes

Measuring

• SI units: metre (m) for length, kilogram (kg) for mass, second (s) for time.
• Vernier calliper: reads lengths to 0.1 mm. Micrometer screw gauge: reads to 0.01 mm, good for wire thickness.
• Measuring cylinder: read the bottom of the curved surface (meniscus) with your eye level with it.
• Scalar and vector: a scalar has size only (speed, mass). A vector has size and direction (velocity, force).

Motion

• Speed: distance divided by time. 150 m in 30 s is 5 m/s.
• Velocity: speed in a stated direction.
• Acceleration: change in velocity divided by time taken. From 2 m/s to 12 m/s in 5 s is 2 m/s².
• Free fall: with no air resistance, every object accelerates downward at about 10 m/s².

Graphs

• Distance-time graph: the gradient is the speed. A flat line means the object is at rest.
• Speed-time graph: the gradient is the acceleration. The area under the line is the distance travelled.