Mechanics Flashcards

1
Q

what is a projectile

A

an object where the only force acting on it is its weight (assuming air resistance has no effect)

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2
Q

is air resistance is negligible what does this mean for forces on the object

A

there is no horizontal forces acting on the object so the horizontal velocity is constant throughout.

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3
Q

how do you calculate horizontal displacement

A

horizontal velocity multipled by time in the air

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4
Q

what is the vertical component in a projectile

A

as weight is the only thing affecting it the acceleration is due to gravity (9.81) gain every second

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5
Q

how can you calculate vertical values on a projectile

A

using SUVAT

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6
Q

how does air resistance change the trajectory of a projectile

A

the horizontal velocity slowly starts to decrease (as there’s air resistance), therefore not travel as far
vertical velocity will gain speed slower

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7
Q

what is friction

A

the force that opposes motion, turning kinetic energy into thermal energy and can never speed things up or start them moving

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8
Q

what are the 2 types of friction

A

contact friction-between 2 solid surfaces
fluid friction- called drag between liquids or gasses

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9
Q

what factors affect drag

A

increases when:
larger surface area
larger speed
larger density

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10
Q

what is lift

A

its an upwards force happening when moving through a fluid, causing the fluid its moving through to change direction

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11
Q

what directions do lift and drag act in

A

lift acts perpendicular to direction of fluid flow and drag acts parallel to it

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12
Q

what 3 things cause lift

A

if the wing diverts air downwards
impact of air on the wing (newtons 3rd law)
Bernoullis principle

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13
Q

what is Bernoullis principle

A

faster air means less pressure so air travelling over the top of the wing travels faster so more pressure is below the wing

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14
Q

what is terminal speed

A

when the frictional forces on an object equal the driving force on an object. there’s is no resultant force and now travels at a constant velocity

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15
Q

what is linear momentum

A

the product of an object’s mass and velocity
its a vector quantity

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16
Q

what’s the principle on conservation of momentum

A

the total momentum before the collision is equal to the total momentum after the collision provided there’s no external forces acting on the object

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17
Q

how does conservation of momentum effect explosions

A

the momentum before is 0, so it has to be 0 after the explosion. this is achieved by loads of fragments flying off in different directions

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18
Q

what is an elastic collision

A

where momentum is conserved as well as kinetic energy.
eg. collisions of air molecules

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19
Q

what is an inelastic collision

A

where momentum is conserved but kinetic energy isn’t conserved mostly lost through heat and sound

20
Q

what is a perfectly inelastic collision

A

where the colliding objects stick together whether they are still moving or not. this is the maximum amount of kinetic energy that can be lost while still conserving momentum
eg. blue tac falling onto a table

21
Q

what happens to the momentum of a single object in a collision

A

the momentum of the single object will change

22
Q

what is change in momentum

A

force is equal to the rate of change of momentum

23
Q

what is impulse

A

the product of force and time/ equal to change in momentum

24
Q

how do you find impulse from a graph

A

the area under a force time graph

25
Q

how do impulse and change in momentum have practical uses in cars

A

crumple zones-by increasing the impact time the force is smaller
airbags- prevent your head from hitting a hard surface and decelerating quickly
seatbelts

26
Q

how do impulse and change in momentum have practical uses in sport

A

in sports like tennis and golf you want the ball to have the greatest velocity.
apply more force
use smaller mass
increase contact time

27
Q

what is work

A

work is done when energy transforms from one form to another

28
Q

what 2 things effect work done

A

the greater the force or the distance the object moved the more work needed to be done

29
Q

how much work does a satellite do

A

none, the force of gravity is perpendicular to the force of motion so it cancels out

30
Q

how can work be found on a graph

A

the area under a force against distance graph

31
Q

what is power

A

the rate of doing work

32
Q

what is the principle of conservation of energy

A

energy cannot be created or destroyed but can be transferred from one form to another. the total amount of energy in a closed system will not change

33
Q

what is efficiency

A

a way of quantifying how much energy is being converted into useful energy, usually expressed as a percentage

34
Q

when would you use SUVAT

A

when acceleration is uniform

35
Q

what are key features of a displacement time graph

A

straight line gradient=velocity
curved line= acceleration (find tangents for velocity)

36
Q

what do different gradients mean on a displacement time graph

A

steep gradient= high velocity
shallow gradient= low velocity
negative gradient= travelling backwards
horizontal gradient= stationary

37
Q

how do you find average velocity on a displacement time graph

A

if the line is very curvy, draw a line of best fit and calculate the gradient from that

38
Q

what are the key features of a velocity time graph

A

gradient= acceleration
area under graph= change in displacement

39
Q

what do different gradients mean on a velocity time graph

A

steep= high acceleration
shallow= low acceleration
horizontal= constant velocity
negative= deceleration

40
Q

what does a curved line mean on a velocity time graph

A

the curve means changing acceleration

41
Q

what is the key feature on an acceleration time graph

A

area under the graph= change in velocity
above x-axis=positive change in velocity
below x-axis= negative change in velocity (slowing down)

42
Q

what is newtons first law

A

if there is no resultant force acting on an object its either at rest or traveling at a constant velocity

43
Q

what is newtons second law

44
Q

what is newtons third law

A

if object A exerts a force on object B, object B exerts and equal and opposite force on object A

45
Q

what is meant by freefall

A

the object only has weight acting on it

46
Q

why do all objects fall at g

A

with no air resistance all objects would accelerate at the same rate and therefore hit the ground at the same time