Chapter 3 - motion and SUVAT Flashcards
formula of average speed
average speed = total distance/total time
key points of a distance time graph
- distance on Y
- time on x
- speed is gradient
- acceleration = increasing gradient
- for instantaneous speed draw a tangent
difference between a vector and a scalar
a vector has a magnitude and direction
a scalar has only a magnitude
equation for velocity
velocity = displacement/time
displacement- time graphs
very similar to distance time graphs but gradient is now velocity
definition of acceleration and equation for acceleration
equation is the rate in change of velocity
acceleration = change in velocity/time
velocity-time graph key points
- gradient = acceleration
- can be +ve or -ve
- area under graph is displacement
SUVAT equation without s
v = u + at
SUVAT equation without a
s = ((u+v)/2 ) x t
SUVAT equation without t
v^2 = u^2 + 2as
SUVAT equation without u
s = vt - 1/2at^2
SUVAT equation without v
s = ut + 1/2at^2
what are the components of stopping distance
stopping distance = thinking distance + braking distance
what is thinking distance
thinking distance is the distance traveled during the driver’s reaction time given by
thinking distance = speed x reaction time
calculating braking distance
suvat can be used to calculate this
B.D. is proportional to V^2
what is meant by an object in free fall
it is accelerating under gravity = 9.81ms^-2
explain the method of determining G using an electromagnet and a trap door
- an electromagnet holds a small steel ball
- when the current is switched off, the ball drops and a timer starts
- the ball falls and hits a flap which stops the timer
- using SUVAT s = 1/2at^2
- this is because our U is 0
explain how the determination of G experiment can be improved using light gates
- The electromagnet and trapdoor may cause delays in the timing
- light gates can be used instead
explain the method of determining G using photos
- a small metal ball is dropped next to a metre rule
- its fall is recorded or photos taken
- the ball’s position at different time period can be used to calculate G by using cumulative distance and time
- plot s against t^2, u = 0 thus gradient = 1/2 g
calculating G graphically
plot s against t^2 and the gradient = G/2
what is the key fact when considering projectile motion
“in projectile motion the horizontal and vertical components are independent of each other”
assuming no air resistance, what can we say about projectile motion
- vertical component only changes due to G
- vertical motion uses SUVAT
- horizontal velocity remains constant and uses d = s x t
vector calculations explained
at any point (if you know the time) the vectors of an object in projectile motion can be calculated, thus the angle can be calculated.
what is a projectile
an object acted upon only by the force of gravity
what is meant by a constant velocity
speed and direction of motion do not change
if an object in water is moving vertically down, what 3 forces are acting on it, thus how does the resultant force change from the object being submerged to reaching its deepest point
upthrust, weight and friction
- resultant force decreases as depth increases because speed decreases so the upwards acting drag force decreases, hence the magnitude of the resultant force decreases
