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A level physics OCR A > Motion > Flashcards

Motion Flashcards

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1
Q

what is the instantaneous velocity

A

the velocity at a given instant in time

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2
Q

what is the average velocity

A

the total displacement divided by the total time taken

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3
Q

how to find the instantaneous velocity from a curved displacement-time graph

A

draw a tangent to the point then find its gradient

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4
Q

whats the velocity of an object bouncing at the very top

A

0m/s

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5
Q

whats the acceleration of a bouncing object

A

g (-9.81m/s^2)

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6
Q

experiment to determin g

A
  1. set up a steel ball and trapdoor
  2. record ball height
  3. open door and time how long it takes to drop (can use pressure plate and electronic timer)
  4. record average of three attempts
  5. measure time form a range of heights
  6. plot a graph of hight against time^2 (should be straight)
  7. calculate g (its the gradient * 2)
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7
Q

what is lift

A

it’s the upward force caused by collisions with air particles on the underside of a wing

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8
Q

how does a plane create lift

A

as it moves forward it pushes air particles down. this causes an equal and opposite upward force on the wings

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9
Q

how are wings shaped and why

A

angled top maximise the amount of air it can push down.

curved and smooth to reduce drag

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10
Q

what is friction

A

the resistance to motion due to contact forces

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11
Q

what does friction do

A

it converts kinetic energy into other types (mostly thermal)

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12
Q

what is drag

A

it’s a frictional force caused by motion in liquids and gases caused by collisions with particles.

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13
Q

factors affecting drag

A

speed of an object
the shape of the object (how streamlined it is)
surface area

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14
Q

what is air resistance

A

the frictional force (drag) opposing the motion of an object travelling through air

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15
Q

how is terminal velocity reached

A

weight stays constant so the downward force doesn’t change. as the objects speed increases the drag increases until it equals the weight. when this occurs the object is at terminal velocity

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16
Q

why do parachutes slow your fall

A

the increased surface area increases air resistance. the resistive force is now greater than the wight. this causes deceleration. the speed decreases and so does the drag until its equal to the weight again. this is at a new slower terminal velocity

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17
Q

factors affecting reaction time

A

drugs/alcohol
fatigue
distractions

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18
Q

how does the velocity of a vehicle change the stopping distance

A

the thinking distance increase linearly with the velocity and the braking distance is proportional to the velocity^2

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19
Q

an important thing about projectile motion?

A

the horizontal and vertical components are independent meaning they are solved separately

20
Q

what forces act on projectiles

A

only gravity. the vertical acceleration is always 9.81m/s^2 and the horizontal is always 0

21
Q

What’s Newton’s first law

A

the velocity of an object won’t change unless a resultant force acts upon it

22
Q

What’s Newton’s second law

A

force and acceleration are directly proportional

23
Q

What’s Newton’s third law

A

when a force acts on an object it applies an equal and opposite force back (for every action there is an equal and opposite reaction)

24
Q

what is the impulse of an object?

A

its change in momentum

25
Q

what is the conservation of momentum?

A

momentum can not be created or destroyed so momentum before a collision = momentum after a collision

26
Q

difference between elastic and inelastic collisions

A

elastic collisions conserve kinetic energy and momentum. inelastic collisions only conserve momentum because some energy is dissipated as thermal or other energy

27
Q

what type of collision is an explosion

A

its a reverse collision. it is an inelastic process as kinetic energy is not conserved. the kinetic energy comes from the internal energy

28
Q

what are some safety features in cars?

A

airbags
crumple zones
seat belts

29
Q

how do safety features of a car work

A

they absorb some of the kinetic energy from a collision. they increase the time taken for the change in momentum to happen, reducing the force

30
Q

definition of a radian

A

the angle between two radii of a circle that are connected with an arc equal to the radii’s length

31
Q

what is the angular speed

A

a measure of how quickly an object’s rotating. the change in angle divided by the change in time

32
Q

whats the period in circular motion

A

the amount of time taken for one resolution

33
Q

whats the frequency in circular motion

A

the number of times it goes around the circle per second

34
Q

why is an object in circular motion always accelerating

A

acceleration is the change in direction or magnitude of velocity. in a circle, the direction is always changing so an object is always accelerating and its always towards the centre of the circle

35
Q

why is the acceleration of circular motion towards the centre

A

the change in velocity is always towards the centre. this is called centripetal acceleration

36
Q

what is centripetal force

A

any force that causes circular motion. the larger the force the smaller the circle. it’s always perpendicular to instantaneous velocity

37
Q

define simple harmonic motion

A

any motion where the acceleration is directed towards a fixed point and is directly proportional to the negative of the displacement

38
Q

whats the gradient of an acceleration-displacement graph

A

the angular frequency (notation- ω) squared by -1. to get the angular frequency square root the
(gradient * -1)

gradient = -1(ω^2)

39
Q

for simple harmonic motion how do acceleration-time graphs and displacement-time graphs differ

A

they are a reflection in the X-axis of each other.

40
Q

how does the GPE, KE and EPE change in a pendulum simple harmonic system

A

at the centre of the oscillation, KE is at a maximum and GPE and EPE are at a minimum. at the top of the oscillation, the GPE and EPE are at a maximum and KE is 0.

41
Q

what is a damping force

A

and force opposing motion (frictional forces)

42
Q

what happens when an oscillation is damped

A

the amplitude decreases. the period and frequency remain the same

43
Q

what are under-damping and over-damping

A

under-damping is when the effects of damping are so minor it would take a long time to see a decrease in amplitude

over-damping causes no oscillations. the object just returns to equilibrium slowly. when the object returns to equilibrium as quickly as possible this is critical-damping

44
Q

how can you find a resonance curve

A

plotting a graph of amplitude against frequency

45
Q

how does damping affect the resonance curve

A

the greater the damping effect is the flatter the resonance curve is

46
Q

when does resonance occur

A

when the applied frequency and natural frequency are similar

A level physics OCR A (15 decks)

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