Motion and forces

Scalar vs vector , units, and drawing

scalar quantity has a magnitude only but vector has magnitude and direction. Vector directions are commonly just states, compass direction, angle, or ±

anything concerning force or displacement, e.g. momentum and velocity are scalar quantities

when drawing vectors there must be arrows, to show direction and length representing magnitude

distance is distance travelled but displacement is exact distance form the starting point

speed and avg speed, typical speeds

• The speed of an object is the distance it travels every second,For objects that are moving with a constant speed : s = d/t

• in (m/s) : walking - 1.5, cycling 6, car, ~20, aero ~225

• some objects in their journey may change speed at certain moments, so where speed isn’t constant : total dist / total time

• velocity is disp/time ∴ direction also given

m , m/s, s

Distance time graph

how distance travelled varies over time, gradient represents speed ∴ 0 gradient = no speed. curved lines : levelling off - deceleration, shooting up - acceleration - graph cannot have a negative gradient bc scalar

displacement is same, but when grad goes down object is moving at a speed backwards - towards starting position, and when hits 0

acceleration , due to g, and typical accelerations of objects, + formula of motion for objects with a constant velocity

• rate of change of velocity - a = ∆v /t , or v-u initial - final velocity, in m/s , m/s² and s (can be ± depending on whether speeding up or slowing down)

• in the absense of frictional forces, the acceleration due to gravity is 10 m/s²

family car is abt 2-3, rocket is 30, and fighter jet is 120

v² - u² = 2ax , where x is distance in m

velocity time graphs

shows how velocity varies with time m = acc.

constant accelerations are straight lines, with their gradients showing magnitude of acc, -m lines are decelerating and lines with no gradient are at a constant velocity, curved lines represent non uniform acc

area under a velocity time graph defines the distance elapsed {[(triangle or rectangle)]}

velocity vector opposite direction problem

velocity is vector but the graph does not represent direction - so if the graph touches 0 again is has not reached its starting position.

For the object to truly reach the starting position, there must be a graph below the x axis to represent - acc, and the area of this graph and the positive graph must be the same

measuring speed methods - electronic + general advantage

1 light gate, clock starts when light is blocked and stop when light goes through again, distance of card is inputted or found

2 light gate - for a set distance the timer measures the time between the gates

ticker timer - taped pulled through a timer that prints dots at specific time intervals, distance between dots used to calk speed, ↑ dist between dots means ↑ speed

electronic methods avoid human reaction time error and ∴ are more precise and accurate