yr 1 mechanics ch 8-9

scalar quantities

only has a magnitude (a size), always positive

vector quantities

have a magnitude and a direction

give the base SI units for:

• mass

• length/displacement

• time

• kg

• m

• s

define and state the units used for:

• displacement

• velocity

• acceleration

• the distance moved in a straight line, in a given direction, from the starting point (m)

• the rate of change of displacement (ms^-1)

• the rate of change of velocity (ms^-2)

distance is the magnitude of which vector?

displacement

speed is the magnitude of which vector?

velocity

displacement-time graphs

• gradient = velocity

• straight line = constant velocity

• curved line sloping up = uniform acceleration

• curved line sloping down = uniform deceleration

• line parallel to t-axis = stationary

• negative gradient = returning to start point

how to calculate average velocity

displacement from starting point / time taken

how to calculate average speed

total distance travelled / time taken

velocity-time graphs

• gradient = acceleration

• straight line = constant acceleration

• line parallel to t-axis = no acceleration = constant velocity

• area between graph and t-axis = total distance travelled

gravity

• causes all objects to accelerate towards the earth

• is constant if you ignore air resistance

• does not depend on the mass of the object

when do we use g = 9.8?

when modelling an object moving vertically in a straight line as a particle: the particle will have a constant downward acceleration of 9.8 ms^-2

how to describe the motion of an object for 2 marks

• accelerating/decelerating

• give direction of travel, e.g.

  • a bearing

  • the angle made with the i or j vector

at overtaking point, what is the same for 2 objects?

displacement