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Physics > P2.3 - Forces In Action > Flashcards

P2.3 - Forces In Action Flashcards

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1
Q

How many forces are needed to change shape of an object

A

2 or more

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2
Q

Plastic material

A

Does not return to its original shape after the force is removed - become deformed or distorted

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3
Q

Elastic material

A

Returns to its original shape after the force is removed

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4
Q

Hooke’s Law

A

Force is directly proportional to extension, within the limit of proportionality

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5
Q

What is limit of proportionality

A

The point beyond which extension is no longer proportional to force

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6
Q

Elastic limit

A

A force beyond which the material will not return to its original shape when the force is removed

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7
Q

Spring constant

A

The ratio of force to extension

Can be said as a measure of the stiffness of a spring

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8
Q

Equation for force exerted by a spring

A

Force (N) = spring constant (N/m) x extension (m)

F = k x e

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9
Q

Equation for energy transferred in stretching

A

Elastic potential Energy (J) = 1/2 x spring constant (N/m) x (extension)^2 (m)

E = 1/2ke^2

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10
Q

Gradient on a force and extension graph

A

Spring constant - the steeper it is the stiffer the spring

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11
Q

area under force extension graph

A

Elastic potential energy

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12
Q

A f.e graph for an elastic band would be non-linear

A

True - therefore doesn’t follow Hooke’s Law :)

good work keep going!

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13
Q

Gravitational field

A

A region where a mass experiences an attractive force

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14
Q

Gravity/weightequation

A

Gravity/weight (N) = mass (kg) x gravitational field strength (N/kg)

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15
Q

What is gravitational field strength (aka gravity constant)

A

measure of the force on a 1kg mass when it is is a gravitational field

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16
Q

What is weight?

A

Force due to gravity which acts upon an object

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17
Q

Gravitational field strength of Earth

A

10 N/kg

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18
Q

Gravitational field strength on the Moon

A

1.6 N/kg

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19
Q

Resultant forces on planet equation

A

Resultant force (N) = Mass (kg) x acceleration due to gravity (m/s^2)

20
Q

What is gravitational potential energy (G.p.e)

A

The energy transferred to a gravity store when you lift an object in a gravitational field

21
Q

G.P.E equation

A

Gpe (J) = mass (kg) x gravitational field strength (N/kg) x height (m)

Gpe = mgh
G.f.s is always 10 on earth

22
Q

Moment

A

The turning effect of a force

23
Q

Moment equation

A

Moment (Nm) = force (N) x PERPENDICULAR distance (m)

24
Q

Moment is a vector

A

True - it is either CLOCKWISE or ANTI-CLOCKWISE

25
Q

What is the moment if the force is applied in line with the pivot?

A

Moment is 0 because it only applies when the force is applied across a PERPENDICULAR distance

26
Q

Perpendicular distance is indirectly proportional to force applied

A

Increase P.distance = proportional decrease in force applied

(Vice versa)

27
Q

Principle of moments

A

When the anti-clockwise moment is the same as the clockwise moment about the pivot

28
Q

On a seesaw where would one with lower mass have to sit?

A

The person with the lower mass would have to sit further away from the pivot and the larger mass would have to sit closer to the pivot

29
Q

Lever

A

A force multiplier which transmits forces by rotating about a pivot. It reverses the direction of the input motion so it is opposite in the output

30
Q

Effort

A

The force that you exert in a lever (the input motion)

31
Q

Load

A

The force that the lever exerts of the load. (The output motion)

32
Q

If load closer to pivot

A

Less force needed (and vice versa)

33
Q

Mechanical advantage

A

Ratio of load to effort

34
Q

Mechanical advantage equation

A

MA (NO UNIT) = load/effort

35
Q

Gears

A

Like moment multipliers

36
Q

Mechanical advantage for GEARS

A

ma = output cog radius/input cog radius

37
Q

What is the perpendicular distance in a cog

A

The diameter

38
Q

If MA < 1

A

Speed multiplier

HOW?

  • big gear goes to small gear
  • lower moment
  • output rotation is faster (because small one turns more within one cycle of the large one)
39
Q

If MA > 1

A

Torque multiplier

HOW?

  • small bear goes to big gear
  • higher moment
  • output rotation slower (because within many cycles on the small one, the big one only does one)
40
Q

How did simple machines revolutionise the way things were done?

A

People were able to complete many tasks easily, using their own effort

41
Q

Pressure in a fluid equation

A

Pressure (Pa) = force @ 90 degrees to surface (N) / area of that surface (m^2)

P = F/a

42
Q

Hydraulic machine

A

A simple machine which uses a liquid to transmit a force

43
Q

Composition of a hydraulic machine

A

2 pistons, a pipe with water- one piston is pushed, pushing the liquid in the pipe and then outputted by the second piston

(Look @ figure 3 on pg 89)

44
Q

If the output piston is larger than the input one

A

Output force is larger

45
Q

If the output piston is smaller than the input piston

A

Output force is smaller

46
Q

Example of hydraulic

A

Car brake

Physics (20 decks)

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