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short physics facts > Forces & Motion > Flashcards

Forces & Motion Flashcards

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1
Q

What is the unit of force

A

Newtons

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2
Q

Equation: Average speed =

A

Average speed = distance / time

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3
Q

Equation: Speed =

A

Speed = distance/time

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4
Q

Equation: Acceleration =

A 
Acceleration = change in velocity/time
a = v-u / t
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5
Q

gradient of a Distance time graph =

A

speed

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6
Q

Gradient of a velocity time graph =

A

acceleration

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7
Q

Area under a velocity time graph =

A

distance travelled

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8
Q

What piece of equipment do you use to measure the speed of an object?

A

a light gate and data logger linked to a computer

Calculates velocity for you

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9
Q

What are the 3 effects of forces?

A

Forces can:
change shape
change speed
change direction

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10
Q

What is the difference between a scalar quantity and a vector quantity?

A

Scalars have size only (eg mass, temp, speed)

Vectors have size and direction (eg force, acceleration, velocity)

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11
Q

If a 6N force acts up on an object and a 10N force acts down, what is the resultant (unbalanced) force?

A

10 - 6 = 4N down

remember always say direction as force is a vector

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12
Q

Equation: Resultant Force F =

A

Resultant F=ma

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13
Q

Equation: Weight W =

A

W = mg

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14
Q

Equation: Stopping distance =

A

Stopping distance = Thinking distance + Braking distance

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15
Q

Factors affecting thinking distance are:

A 
Speed
Increased reaction time caused by:
distractions
drugs/alcohol
visibility
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16
Q

Factors affecting braking distance:

A

Speed
Mass
Wet/slippery road
Worn tyres and brakes

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17
Q

Describe the motion of a falling object (eg a skydiver)

A

At start, weight force great than air resistance
This unbalanced force causes acceleration
As speed increases, air resistance increases
But weight stays the same
So Unbalanced force decreases so does acceleration
Until Weight = air resistance
Terminal velocity is reached

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18
Q

What is the force that always opposes motion?

A

Friction

19
Q

What is the force between two magnets?

A

Magnetic force

20
Q

What is the force between two charges?

A

Electrostatic force

21
Q

What is the force in a stretched rope?

A

Tension force

22
Q

What is the force acting up on a wing of a bird or plane?

A

Lift force

23
Q

What is the force pulling an object towards the earth?

A

Gravitational (also called weight)

24
Q

What is the force acting upwards on a floating object?

A

Upthrust

25
Q

What is the force acting against a moving car?

A

Air resistance (also called drag)

26
Q

What is the force acting against a moving fish?

A

Drag

27
Q

Moment of a force =

A

Force x perpendicular distance force to pivot

28
Q

Force on a spring or wire

F =

A

F = kx

x is extension
k is spring constant

29
Q

What features of a load vs extension graph tells you the spring obeys Hookes Law?

A

Straight line graph through the origin

30
Q

Describe elastic behaviour

A

Ability of a material to return to original shape when extending force is removed

31
Q

What is centre of gravity?

A

Point through which all the weight appears to act

32
Q

What is the Principle of moments?

A

In equilibrium,

Total moment clockwise = Total moment anti-clockwise

33
Q

Hooked law states….

A

Extension is directly proportional to load

Load force F = kx

34
Q

How can you tell by looking at the force extension graph for a stretched wire that is obeys Hooke’s Law

A

straight line through the origin

F = kx extension is directly proportional to load

35
Q

Describe an experiment to investigate how extension varies with load on a srping, wire or rubber band.

A

Measure original length
Add weight
Measure new length
Calculate extension = new length - original
Add another weight
Continue until you have a good range of readings.
Repeat by unlaoding and measuring extension.
Avoid parallax by having spring and ruler close together

36
Q

Eqn of motion v2 =

A

v2 = u2 + 2as

37
Q

Momentum p =

A 
momentum = mass x velocity
p = mv
38
Q

Principle of conservation of momentum

A

in a collision or explosion

total momentum before = total momentum after

39
Q

Equation linking force and momentum

A

Force = change in momentum/time

F = m (v-u) / t

40
Q

Impulse = change in momentum

Impulse =

A 
impulse = force x time
Impulse = Fxt
41
Q

How to safety features such as set belts and air bags reduce risk of injury?

A

They increase the time to change the momentum of the passenger.
As Force = change in momentum/time,
time increases to change momentum so force is reduced.
Less injury.

42
Q

State Newton’s Third Law

A

If object A exerts a force on object B

then object B exerts an equal and oppostie force on object A

43
Q

What is true about Newton Third Law pairs of forces

A

Same size
Opposite direction
Same type of force
Act on different objects

short physics facts (10 decks)

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