PHYSICS- kinematics

kinematics

• key words:
• - displacement: distance moved in a particular direction
• - speed: average speed is distance moved in time taken
• - mean speed: total distance traveled over total time taken
• - acceleration: the rate of change of velocity (rate means divided by time)
• - velocity: speed of something in a given direction
• - instantaneous speed: value of the speed off an object at a particular time
• if a question said " determine the speed at 6.0s " you would draw a tangent at that point and work out the speed
• by using change in y/ change in
• CHANGE IN DIRECTION > CHANGE IN VELOCITY > CHANGE IN ACCELERATION
• + A change in speed, direction means that the object has a change in velocity
• + in physics if you turn a corner , and your speed is constant-- your velocity still changes.
• + To maximize your velocity you displace more from your original position

distance time graph

speed time graphs

• 
• method for working out instantaneous acceleration:
• >draw a tangent at a specific point
• =change in y/change in x
• the gradient will be the acceleration
• Method for working out the distance travelled
• >area under the curve
• X x Y/2 (for a triangle)
• X x Y (for a rectangle)
• speed x time = distance

displacement time graphs

• displacement is the distance of how far the object has moved from the original position
• a displacement time graph represents how the position of an object relative to a fixed position changes as time progresses
• ~the gradient of a displacement time graph is VELOCITY
• A d-t is a curve
• The area under the curve has no meaning
• it shows the amount it has displaced from its original position, even if it is going towards the position it is still displacing itself.

velocity time graphs

• The gradient of a velocity time graph is ACCELERATION
• >the steeper the slope the higher acceleration
• >FORWARDS (positive numbers)- if the slope is + its accelerating
• - if the slope is - its decelerating
• >BACKWARDS(negative numbers)-if the slope is + its decelerating
• - if the slope is -, it is accelerating
• >CHANGES DIRECTION WHEN IT CROSSES X AXIS
• 

acceleration time graphs

• logic that all freely falling objects ( in the absence of air resistance) accelerate to earth with the same acceleration.
• ACCELERATION DUE TO GRAVITY- 9.1ms-1

equations of motion

• ~~ these are only used when acceleration is constant~~
• Acceleration = change in velocity
• time taken
• A=V-U
• T
• We can rearrange this formula to make V the subject of the formula
• V= U + AT
• the area under the curve is DISPLACEMENT=(area of trapezium)
• S= 1 ( U + V ) x T
• 2
• 

equations of motion...

• we can combine
• V = U + AT and S = 1 ( U + V ) x T
• 2
• substitute v= u + at into the other formula
• S = 1 (U + U + AT) x T
• 2
• S = 1 (2U + AT) x T
• 2
• S = 1 (2U + AT ^2) S = 1 2 UT + 1 AT^2
• 2 2 2
• S= UT + 1 AT ^2
• 2
• now we can combine S= UT + 1 AT ^2
• 2
• and V = U + AT to make V^2 = U^2+ 2AS
• V^2 = (U + AT)^2
• = U^2 + 2U AT + A^2 T^2
• = U^2 +2A( UT +1/2 AT^2)
• = U^2 +2AS
• V= FINAL VELOCITY
• U= INITIAL VELOCITY
• A= ACCELERATION
• S= DISPLACEMENT
• T= TIME

Slide 9

S.U.V.A.T

• SUVAT is a technnique used that applies all the four different equations of motion
• S= dislacement (m) sometimes called X in exams
• U= inital speed (ms-1)
• V= final speed (ms-1)
• A= acceleration (ms-2)
• T= time (s)

vertical motion under gravity

converting from v-t to d-t graphs

• on a velocity time graph when it passes through the origin it means it chnaged direction BUT on a d-t graph it doesnt matter if it changes direction it is still moving and accelerating.
• >if it is decelerating the curve on the d-t graph will just flatten out