G481, Mechanics Physics revision notes

Revision notes after reading through each chapter of the OCR textbook and revision books accosiated. Includes some general key elements to know about the subject. includes some ref. to pages in the blue 'Physics for OCR 1' textbook Gurinder Chadha & David Sang.

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Page 1

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Physics- mechanics




Kinematics, describing motion

Average speed = d
t

Uniform motion:
displacement
(ms¹) Velocity = time (Rate of change of displacement)




Vector quantity ­ magnitude (size) and direction. (E.g. Velocity, displacement)
Scalar quantity ­ magnitude (size) only. (E.g. Distance, speed)

Displacement/time graphs:




Gradient shows velocity (change in displacement)
Straight…

Page 2

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Physics- mechanics




Accelerated Motion

(ms²) Acceleration= Change in V elocity
time taken OR (a= V
t ) OR (a= [v-u]
t )

(Rate of change of velocity.)




Gradient shows acceleration.
Steeper the gradient, greater the acceleration.

s
V= t rearrange to be s = v×t ­area under v/t graph shows…

Page 3

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Physics- mechanics




a = acceleration
t = time
v-u
v = u + at .....rearrangement of a= t

v+u
s= 2 ×t .....says displacement = average velocity x time.

2 1 2
s = ut + 1
2 at (Zero acceleration, becomes displacement = velocity x time) s = vt…

Page 4

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Physics- mechanics




An object will remain at rest or in a state of uniform motion unless it is acted on
by an external force.....
....Balanced forces (on an object) ­ object remains at rest or continues to move with
constant velocity.
Unbalanced forces ­ motion will change, therefore acceleration in…

Page 5

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Physics- mechanics




-absence of air resistance, horizontal component of v is constant while vertical component
of v downwards increases at a rate of 9.81ms²

-STATE POSSITIVE DIRECTION, when a ball is thrown upwards, positive direction can be as it
travels upward then negative as it falls to earth, then initial…

Page 6

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Physics- mechanics




In a right angled triangle, use Pythagoras' theorem to calculate resultant.




can be found with two known lengths AB and BC.

Resolving:
-break down components to 90° of one another.

E.g.)




Perpendicular components are independent of one another; changing one doesn't affect the other.




Adding perpendicular components

Forces…

Page 7

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Physics- mechanics




There is no `resultant force' the forces on the spider balance, in equilibrium.




Forces, moments and pressure
important to consider the forces acting on an object, enabling us to predict how the object
is moving.
Pushes & pulls, weight, friction, drag, up thrust, contact force, tension.

Page 8

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Physics- mechanics




Moment of a force tell us about the turning effect
defined as:
Moment (Nm) = magnitude of the force (N) x perpendicular distance of its line of
action from the pivot (m)




Principal of moments:
For any object that is in equilibrium, the sum of the clockwise moments…

Page 9

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Physics- mechanics




Torque of a couple = magnitude of one force x perpendicular distance between the
forces.




Equilibrium:
for an object to be in equilibrium, two conditions are met at the same time:

Must be no resultant (unbalanced) force acting on it/equalling zero;
Must be no resultant torque acting on…

Page 10

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Physics- mechanics




Stopping distance = thinking distance + braking distance.




Factors affecting stopping distance:

Thinking distance depends on speed and thinking time/condition of the driver.
-Greater vehicle speed, greater thinking time.
-Age (reactions are slower)
-Influence of drugs (alcohol recreational, medical)
-Tiredness

Breaking distance depends on physics speed of the…

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Hannah

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thank you, this helps so much! :)

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