P2.3 - Forces In Action Flashcards

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
What is the moment if the force is applied in line with the pivot?
Moment is 0 because it only applies when the force is applied across a PERPENDICULAR distance
26
Perpendicular distance is indirectly proportional to force applied
Increase P.distance = proportional decrease in force applied (Vice versa)
27
Principle of moments
When the anti-clockwise moment is the same as the clockwise moment about the pivot
28
On a seesaw where would one with lower mass have to sit?
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
Lever
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
Effort
The force that you exert in a lever (the input motion)
31
Load
The force that the lever exerts of the load. (The output motion)
32
If load closer to pivot
Less force needed (and vice versa)
33
Mechanical advantage
Ratio of load to effort
34
Mechanical advantage equation
MA (NO UNIT) = load/effort
35
Gears
Like moment multipliers
36
Mechanical advantage for GEARS
ma = output cog radius/input cog radius
37
What is the perpendicular distance in a cog
The diameter
38
If MA < 1
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
If MA > 1
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
How did simple machines revolutionise the way things were done?
People were able to complete many tasks easily, using their own effort
41
Pressure in a fluid equation
Pressure (Pa) = force @ 90 degrees to surface (N) / area of that surface (m^2) P = F/a
42
Hydraulic machine
A simple machine which uses a liquid to transmit a force
43
Composition of a hydraulic machine
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
If the output piston is larger than the input one
Output force is larger
45
If the output piston is smaller than the input piston
Output force is smaller
46
Example of hydraulic
Car brake