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Physics > Forces > Flashcards

Forces Flashcards

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AP® Physics flashcards Physics 101 flashcards
1
Q

a vector has…
a scalar has…

A

magnitude and direction
just magnitude

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2
Q

… cannot be negative but… can

A

scalars
vectors

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3
Q

examples of scalar

A

speed
distance
time
mass
energy

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4
Q

examples of vector

A

velocity
displacement
acceleration
force
momentum

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5
Q

what is scalar

A

can be measured with a number (magnitude)

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6
Q

what is a vector quantity

A
  • measured with a number
  • BUT ALSO
  • has a direction
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7
Q

gravity- the larger the… the stronger the… the greater the…

A

mass
field
attraction

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8
Q

weight calculation

A

weight = mass x gravitational field strength

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9
Q

weight is measured using a… by…

A

force meter / calibrated spring-balance
by the weighing scales measuring the force you exert then divides by 10 to get the mass

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10
Q

gravitational field strength on earth

A

9.8

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11
Q

what happens to mass and weight of the same person on two different planets

A

mass stays the same
wieght is different because gravitational field strength is different

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12
Q

skydiver example of resultant forces

A
  1. initially, there is no air reisstance so only force acting on him is weight = accelerates
  2. air resistance increases, resultant force from weight decreases= acceleration decreases
  3. eventually equal and balance, so no resultant force = no acceleration
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13
Q

work done =

A

work done = force x distance

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14
Q

one joule of work is done when…

A

a force of one newton causes a displacement of one metre
1 joule = 1 newton metre

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15
Q

to stretch, bend of compress an object… need to be applied otherwise…

A

multiple forces need to be applied otherwise it will just move in one direction

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16
Q

elastic deformation

A

the object returns to its original shape when the load has been removed

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17
Q

plastic deformation

A

the object does not reutrn to its original shape when the load has been removed, this can be a spring when pulled too far

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18
Q

Hooke’s law

A

the extension of an elastic object, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded

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19
Q

hooke’s law calculation

A

F = kx
Force = spring constant x extension
N Nm-1 m

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20
Q

hooke’s law : why does the graph stop being linear

A
  • the limit of proportionality has been reached, no longer obeys hooke’s law
  • turns to plastic behaviour (object pulled too far)
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21
Q

hooke’s law: if the graph is just linear with no non-linear end seciton…

A

… the material is brittle, so snaps instead of stretching afte tthe elastic limit

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22
Q

work done (spring) calc

A

work done = 1/2 x spring constant x extension squared

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23
Q

the work done on the spring =

A

= the elastic potential energy stored

24
Q

moment of a force =

A

moment of a force = force x perpendicular distance
M = Fd

25
Q

(roations and moments)equilibrium is when…

A

sum of anticlockwise moments = sum of clockwise moments

26
Q

Gears: if a gear (1) is connected to another gear (2)with fewer teeth (smaller)

A
  • second gear with turn faster
  • but with less force
  • in opposite direction to first gear
27
Q

if a gear (1) is connected to a gear (2) with more teeth (larger)

A
  • turns slower
  • more force
  • in opposite direction
28
Q

pressure calc

A

pressure = force / area

29
Q

pressure in fluids: an object floats if its weight is…

A

less than the weight of the water it displaces

30
Q

buoyancy is the…

A

upwards force that counteracts the weight of the floating object

31
Q

objects that float have a lower…

A

density than the water so the weight of the equivalent amount of water is greater than the weight of the floating object

32
Q

pressure due to a column of liquuid =

A

pressure due to a column of liquid = height of column x density of liquid x gravitational field strength

p = hpg

33
Q

upthrust (liquid)

A
  • a partially or totally submerged object experiences a greater pressure on the bottom surfacr than the top surface
  • this creates a resultant force upwards (upthrust)
34
Q

earth’s atmosphere

A

thin layer on air around the earth which gets less dense with increasing altitude

35
Q

explain why there the atmosphere gets less dense with increasing altitude

A
  • the weight of the air is the force which causes the pressure
  • so higher up, there are fewer air molecules than lower down
  • so smaller weight so less pressure
36
Q

assumptions made for a simple modle of the atmosphere

A
  • isothermal (all at the same temp)
  • transparent to solar radiation
  • opaque to terrestrial radiation
37
Q

if an object is moving in a circular motion, the acceleration… because…

A

increases because changing velocity is defines as acceleration so the change in direction means it accelerates

38
Q

speed equation

A

speed = distance/ time

39
Q

displacement time graphs:
- sharper gadient means…
- negative gradient means…
- horizontal line means…
- curved line means…

A

sharper gradient = faster speed
negative gradient = returning back to starting point
horizontal line = stationary
curved line = velocity is changing

40
Q

velocity-time graphs:
gradient is…
sharper gradient means…
negative gradient means…
horizontal line means…
0 velocity means…
curved line means…

A

gradient is acceleration
sharper gradient is greater acceleration
negative gradient is deceleration
horizontal line is constant speed
0 velocity is stationary
curved line means acceleration is changing

41
Q

falling in a fluid

A
  1. initially object will fall under gravity
  2. but then the drag forces will act and the object will move at terminal velocity
42
Q

Netwtons first law

A

an object has a constant velocity unless acted on by a resultant force

43
Q

Newton’s second law

A

the acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object.

44
Q

equation linking force, acceleration and mass

A

force = mass x acceleration

45
Q

inertia

A

the measure of how difficult it is to change the velocity of an object

46
Q

inertial mass =

A

inertial mass = force/ acceleration

47
Q

newton’s third law

A

whenever two objects interact, the forces they exert on each other are equal and opposite

48
Q

vehicle stopping distances

A
  1. after seeing a hazard, there is reaction time during which you travel x metres (thinking distance)
  2. then you react, causing the car to slow down and stop over y metres (braking distance)
49
Q

to find reaction time… (practical)

A

ruler drop test

50
Q

when a force is applied to the brakes of a vehicle…

A
  1. energy is transferred (by friction) to the wheel
  2. so the vehicle’s kinetic energy decreases
  3. and temp on the brakes increase
51
Q

momentum =

A

momentum = mass x velocity
p = mv

52
Q

momentum is always conserved in a…

A

collision or explosion (where there ar eno external forces like air resistance etc)

53
Q

equation linking force, time and change in momentum

A

force = change in momentum / time

54
Q

Safety features in cars - seatbelts

A
  1. seatbelts - stretch under large forces, stretching increases distance move slightly but extends the time taken for passengers to stop, decreases rate of change of momentum and therefore reduces force
55
Q

safety features in cars - crumple zones

A
  • without them cards would be a solid metal block which stops immediately
  • softer areas at the front of the car which crumple upon a crash
  • absorbs energy to deform and compact
  • increases time taken for car to stop therefore reduced acceleration and force on passengers
56
Q

safety features in cars - air bags

A
  • without these your head would whip forward hitting the steering wheel
  • inflates insantly upon a crash
  • your head hitd this and slows down
  • increases time taken for head to stop moving so reduces force on neck

Physics (10 decks)

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