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BMAT Physics > mechanics > Flashcards

mechanics Flashcards

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1
Q

scalar quantities

A
  • quantities that have magnitude (size), but not direction

- e.g. mass, energy, pressure, temp, power, speed, distance, time

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2
Q

vector quantities

A
  • quantities that have both magnitude (size) and direction

- e.g. displacement, acceleration, velocity, force, momentum

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3
Q

an accelerating object can be moving at a constant speed if…

A

it is changing direction constantly

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4
Q

displacement

A

the shortest distance from one point to another in a particular direction

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5
Q

acceleration=

A

(final velocity - initial velocity) /time

  • units : ms-2
  • direction is the same as the direction of the change in velocity
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6
Q

distance-time graphs

A
  • can only be +ve, line cannot go down

- the gradient at a point = the speed at that point

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7
Q

displacement-time graphs

A
  • zero value (on x-axis): at starting point
  • +ve value (above x-axis): at +ve side of starting point
  • -ve value (below x-axis): at -ve side of starting point
  • flat line: stationary
  • ascending line: moving in +ve direction
  • descending line: moving in -ve direction
  • exponential increasing line: increasing velocity
  • exponential decreasing line: decreasing velocity
  • the gradient at a point = the velocity at that point
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8
Q

velocity-time graphs

A
  • zero value (on x-axis): stationary
  • flat line: constant velocity
  • ascending line: accelerating in +ve direction
  • descending line: accelerating in -ve direction
  • exponential increasing line: increasing acceleration
  • exponential decreasing line: decreasing acceleration
  • the gradient at a point = the acceleration at that point
  • area under graph = change in displacement
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9
Q

speed-time graphs

A
  • can only be +ve

- area under graph = distance travelled

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10
Q

equations of motion

A
  • s=0.5(u+v)t
  • 𝑠=ut + 0.5at^2
  • v^2=𝑢^2+2𝑎𝑠
  • average v = 0.5(u+v)
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11
Q

forces

A
  • the application of a push or a pull to an object by another object
  • vector quantity,
  • units: newtons (N)
  • types: weight, normal contact, drag, friction, magnetic, electrostatic, upthrust, thrust, lift and tension
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12
Q

force formulae

A 
F=ma
F=momentum/time
P=F/a
moment=F x perpendicular distance
Ew = F x displacement
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13
Q

weight formula

A

W=mg
W=weight in N
m=mass in kg
g=gravitational field strength in Nkg-1 (9.8 on Earth)

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14
Q

normal contact force

A

-force as a result of 2 solid objects being in contact with each other

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15
Q

tension

A
  • when a spring/string/wire is pulled by equal and opposite external forces at each end as shown, it is said to be subjected to a tension force, 𝑇
  • this tension force usually causes the length of the spring/string wire to increase slightly.
  • the increase in length = the extension
  • the greater the tension force, the greater the extension
  • T=weight=mg
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16
Q

force-extension graphs

A
  • the steeper the graph, the greater the spring constant -> more rigid
  • the shallower the graph, the greater the spring constant -> less rigid
  • work done by this force = the area under the graph
17
Q

material types

A
  • copper wire stretches uniformly initially, but then suddenly stretches much more just before reaching the breaking point
  • glass is very rigid and deforms only very slightly before breaking
  • rubber stretches non-uniformly
18
Q

deformation

A
  • elastic deformation is reversed when the force is removed
  • inelastic deformation is not fully reversed when the force is removed (permanent stretching)
  • materials that undergo permanent stretching are ductile
19
Q

elastic limit

A

-the point on the force-extension graph where the extension goes from being elastic to inelastic (when the line on the graph starts to flatten)

20
Q

Hooke’s Law

A

F=kx

  • F=force applied to the material/spring (N)
  • x=extension of the material/spring (m)
  • k=spring constant, a measure of the stiffness of a spring up to its elastic limit, high k->rigid (Nm-1)
21
Q

factors affecting spring constant

A
  • the greater the cross-sectional area, the greater the spring constant
  • the longer the wire, the smaller the spring constant
22
Q

combining springs

A
  • if 2 springs are connected together in series, then it double the extension -> spring constant is = 0.5𝑘.
  • if 2 springs are connected in parallel, then it will double the force -> spring constant = 2𝑘
23
Q

momentum formula

A

p = mv

  • p=momentum (kg/ms-1 or Ns)
  • m=mass (kg)
  • v=velocity (ms-1)
24
Q

newton’s first law

A

an object will remain at rest or move with constant velocity in a straight line unless acted upon by an unbalanced force

25
Q

newton’s second law

A

when a constant unbalanced force is applied to an object, the object will move with constant acceleration in the direction of the unbalanced force

26
Q

newton’s third law

A

to every action there is an equal and opposite reaction

27
Q

gravitational field strengths

A
  • the magnitude of the gravitational force acting per unit mass of an object in the field
  • Earth: 10Nkg-1
  • Moon: 1.6Nkg-1
  • Jupiter: 26Nkg-1
28
Q

acceleration of free-fall

A

an object falling freely due to gravity falls with an acceleration that is numerically equal to the gravitational field strength

29
Q

factors affecting air resistance

A
  • increasing speed of motion increases air resistance
  • increasing cross-sectional area of the object, increases air resistance.
  • turbulent air flow gives greater air resistance force compared to streamlined air flow
30
Q

terminal velocity

A
  • the speed at which air resistance = weight

- vertical forces acting upon an object are balanced

31
Q

power formulae

A
  • P=E/t
  • P=work done/time
  • P=F x velocity
32
Q

kilowatt-hour

A

1kWh=3600kJ

33
Q

stored and active energy

A

active:
- electrical
- heat (thermal energy)
- light
- kinetic
- sound
stored:
- chemical potential energy (stored in a battery/cell)
- gravitational potential energy (stored due to height)
- strain potential (energy stored in a stretched spring)

34
Q

energy formulae

A
  • % efficiency = (useful energy/stored energy) x100
  • Ek = 0.5mv^2
  • Ep = mgh
  • total energy = Ep/Ek + work done against frictional force
35
Q

conservation of momentum (working out velocity of object B after a collision)

A
  1. work out total momentum before the collision (momentum of object A + momentum of object B)
  2. this will also be the total momentum after the collision
  3. work out the total mass after the collision (mass of object A + mass of object B)
  4. work out velocity of object B using v=p/m
36
Q

moment of a force about a point formula

A

T=Fd

  • T=moment of a force (Nm)
  • F=force (N)
  • d=perpendicular distance from pivot to the line of action of the force (m)

BMAT Physics (7 decks)

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