Physics- Motion Flashcards
Speed (m/s)
How fast something is moving regardless of direction
Displacement (s)
How far an object’s travelled from its starting point in a given direction.
Velocity (v)
The rate of change of an object’s displacement (its speed in a given direction)
Acceleration (a)
Rate of change of an objects velocity
Acceleration formula
Acceleration is the rate of change of velocity.
1.)a=(v-u)/t so v=u + at
2.)s= average velocity x time acceleration constant, the average velocity is average initial and final so (u+v)/2 x t
3.) Sub expression for v from equation 1 into 2 gives s=(u + u + at) x t /2
s = ut + 1/2at^2
4.)derive a = (v-u)/2 multiply by s, s= (u+v)/2 x t gives as=(v-u)/2 x (u+v)t/2 ts cancel so 2as= (v-u)(v+u) or 2as=v^2 -uv+uv -u^2
v^2=u^2 + 2as
Uniform Acceleration
Constant Acceleration
Suvat Equations
V=u+at
S=vt-1/2at^2
S=ut+1/2at^2
S=1/2(u+v)t
V^2=u^2+2as
Average Speed
= Total distance/ Total time
Average Velocity
= Total displacement/ Total time
Instantaneous Velocity
Velocity at a particular point in time.
The gradient of the tangent in a displacement/time graph.
Acceleration
The rate of change of velocity
The area under a velocity time graph
Is the displacement
If the acceleration is in the direction of motion
It is positive.
If the acceleration is opposite to the direction of motion
it is negative.(deceleration)
Vertical acceleration
9.81ms^-2
If an object is projected upwards
An acceleration of -9.81ms^-2 acts upon it. (gravity)
Give the manual timing PAG method to determining g.
Drop a marble form different heights,
record the time it takes to reach the ground.
Measure the height, h with a ruler,
Measure the time,t, with a stopclock or a video (phone)
Plot a graph of the h against t^2
Use SUVAT s+ut+1/2at^2
Derive into S=1/2at^2
h=1/2 gt^2
TO REDUCE PERCENTAGE UNCERTAINTIES
Make sure that h is as large as impossible,
Use a trapdoor or electro magnet so the time is consistently and height remains the same as human error is not involved. Certainty ^^
Light gate Method
2 light gates
Measure initial velocity and light gate 2 to measure final
measure distance between two with ruler v^2=u^2+2as
Stopping distance
= thinking distance + braking distance
Thinking distance
defined as the distance travelled by the vehicle from the moment a driver spots a hazard to the time they press the brake pedal
Braking distance
Distance from the moment the driver presses the brake pedal to the moment the car stops.
Braking distance equation
v^2=u^2+2as
0=u^2+2aSb
Sb= -u^2/2a
(a negative because its deceleration)
Thinking distance equation
speed x time
