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Physics > Topics 1&2: Forces And Motion > Flashcards

Topics 1&2: Forces And Motion Flashcards

1
Q

What are common units for speed?

A

Meters per second (m/s)

Kilometres per hours (km/h)

Miles (mph)

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2
Q

How can speed be calculated?

A

Speed=distance/time

s=d/t
d=s x t
t =d/s

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3
Q

What do light gates do?

A

To measure speed in a laboratory you need to measure a distance and time. For fast moving objects using a light gate to measure time is more accurate than a stop watch.

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4
Q

Examples of some average speeds:

A 
Airliner - 250m/s
High speed train - 90m/s
Commuter train - 55m/s
Motorway speed limit - 31m/s
Ferry- 18m/s
Speed limit in towns -10.5m/s
Cycling - 6m/s
Walking - 1.4m/s
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5
Q

How can a journey be recorded?

A

A distance/time graph. Since distance and time can be used to calculate speed the graph can tell us different things.

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6
Q

What can a distance time graph tell us about speed?

A
  • horizontal line means the object is stationary.
  • straight sloping line means object is travelling at a constant speed.
  • steeper the lone the faster the object is travelling.
  • the speed is calculated from the gradient of the line.
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7
Q

What is weight?

A

Weight is the force that acts towards the centre of the Earth.

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8
Q

What do all forces have?

A

Forces have both a magnitude and a direction and are measured in newtons (N). Forces are vectors.

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9
Q

What is a vector and give some examples of vector quantities:

A 
Quantities that have both size and direction. 
Examples of vectors are:
-force
-velocity 
-acceleration
-momentum
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10
Q

What is mass?

A

Mass measure the amount of matter in an object. It does not have a direction and is measured in (Kg). It only changes if the quantity if the object itself changes. E.g your mass increases if you eat a meal.

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11
Q

What is a scalar quantity and give examples of some scalar quantities:

A

Scalar quantities have magnitude only.

Examples are:

  • time
  • distance
  • speed
  • energy
  • mass
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12
Q

What is displacement?

A

The distance covered in a straight line, and has a direction. The displacement at the end of the journey is usually less than the distance travelled because of the turns and or bends in the journey.

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13
Q

What is velocity?

A

Velocity is speed in a particular direction.

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14
Q

What are acceleration and momentum classified as and what do they mean?

A

Acceleration and momentum are both vector quantities.

Acceleration: a measure of how fast velocity is changing.
Momentum: a combination of mass and velocity

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15
Q

What is acceleration?

A

A change in velocity. Acceleration is a vector quantity. If a moving object changes its velocity or direction then its accelerating.

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16
Q

What does acceleration tell you and what are the units for it?

A

It tells you the change in velocity each second, so the units for acceleration are meters per second per second. (m/s2)

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17
Q

How is acceleration calculated?

A

Acceleration = change in velocity/time taken

a= v - u / t

a= acceleration v= final velocity u= initial velocity t= time taken

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18
Q

What is deceleration?

A

Acceleration does not mean getting faster. An acceleration can also cause an object to get slower. This is called deceleration, and the acceleration will have a negative value.

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19
Q

How can acceleration be related to initial velocity, final velocity and distance traveled by equation.

A

(Final velocity)2 -(initial velocity)2 = 2 x acceleration x distance

V squared - U squared = 2 x a x X

X represents distance

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20
Q

What is the force (acceleration) of gravity on earth?

A

9.8 m/s squared. The symbol can be represented by a g and can be rounded to 10m/s squared.

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21
Q

What do velocity time graphs show?

A
  • A horizontal line means the object is travelling at a constant velocity.
  • A sloping line shows that the object is accelerating. The stepper the line, the greater the acceleration. If the line slopes down to the right, the object is decelerating. You can find the acceleration of an object from the gradient of the line on the graph.
  • a negative velocity (a line below the horizontal axis) shows the object moving in the opposite direction.
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22
Q

What is the area under the velocity time graph?

A

This is the distance the object has travelled. You can do this by splitting the graph into shapes such as rectangles, squares and triangles to work out the area.

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23
Q

What happens when an object changes its velocity?

A

It accelerates. Acceleration is a change in velocity so is a vector quantity.

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24
Q

Are forces a vector quantity?

A

Yes

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25
What does the arrow describing a force tell us?
The magnitude of the force and the direction it is acting in. The size of the force is represented by the length of the arrow.
26
How do you work out the resultant force of 2 forces?
If the forces are acting in the same direction add them | If they are acting in opposite directions subtract one from the other.
27
What is the resultant force?
The total force of two or more forces acting upon a single object. It is found by adding together the forces acting in the same direction and subtracting ones in the opposite direction. It is also known as net force.
28
What happens if the resultant force is zero?
This means the forces in the object are balanced. If the resultant force is not zero the forces are unbalanced and will have a resultant force.
29
What is Newton’s first law?
A moving object will continue to move at the same speed and direction unless an external force acts on it. A stationary object will remain at rest until an external force acts on it.
30
What is important when you are looking at how the velocity of an object changes?
The overall resultant force. Balanced forces will not change the velocity of an object. Unbalanced forces will change the speed or direction of an object.
31
What is centripetal force?
A force that causes objects to follow a circular path. The force acts towards the centre of the circle.
32
What happens to the velocity in centripetal force?
The velocity is constantly changing (even if the speed is the same the direction is constantly changing). The resultant force that causes this change is centripetal force.
33
What does weight depend on?
The strength of gravity pulling in an object.
34
How can weight be measured?
Using a force meter which has a scale in Newton’s.
35
How does a force meter work?
Force meters contain a spring a spring which stretches as the force on it increases allowing the weight to be read of a scale.
36
What is the gravitational field on earth.
The gravitational field is about 10 N/Kg. More specifically 9.8N/Kg This means that each kilogram is pulled down with a force of 10N. The gravitational field is different on other planets and moons.
37
What is equation for gravitational field strength?
Weight = mass x gravitational field strength (N) (Kg) (N/Kg) W = m x g
38
What is terminal velocity?
When resultant force going down = air resistance..........you have reached terminal velocity.
39
What happens when there are no forces acting on two objects on being heavy (e.g bowling ball) and one being light (e.g feather).
When dripped form a height the bowling ball will accelerate faster due to its larger mass and reach the ground quicker. The feather will reach the ground after as it has more forces acting on it and the air resistance is greater. When all the air is taken out the (chamber) they will accelerate at the same speed and reach the ground at the same time due to no forces acting on either of them and they will both have the same gravitational field strength of 10N/Kg.
40
What is Newton’s second law?
The acceleration of in the direction of the resultant force depends on: - the size of the force (for the same mass, the bigger the force the bigger the acceleration) - the mass of the object (for the same force, the more massive the object the smaller the acceleration)
41
What is the equation for force?
Force = mass x acceleration (N) (Kg) (m/s squared) F = m x a (1 Newton is the force needed to accelerate a mass of 1kg by 1m/s squared)
42
What is inertial mass?
The inertial mass of an object is the force on it divided by the acceleration that forces produce.
43
What happens to force depending on the mass of the object?
The more massive an object is the more force is needed to ch age the velocity. (Make it start moving or change the velocity of a moving object)
44
What values do you get when calculating an objects inertial mass?
Calculating an objects inertial mass of an object from values of force and acceleration gives the same mass value as that found by measuring the force of gravity on it.
45
What is Newton’s third law about?
Newton’s third law is about the forces on two different objects when they interact with each other. This can be described as ‘action reaction pairs’. This can happen when: - Objects touch (e.g when you sit down on the chair) - at a distance such as gravitational attraction between the Earth and the moon.
46
What are action reaction pairs?
There is always a pair of forces acting on two interactive objects called action reaction pairs. The two forces are always the same size and acting in opposite directions. They are also the same type of force.
47
What is an equilibrium situation?
When nothing is moving.
48
In an equilibrium situation the action reaction force are not the same as balanced forces. It may be that the sizes of forces are equal and in opposite directions, but:
The action reaction force act in different objects. | Balanced forces all act on the same object.
49
What happens to action reaction forces during a collision?
They action reaction forces that occur during a collision are the same size but they do not necessarily have the same effects on the two objects because the objects have different masses.
50
What is momentum?
Momentum is a measure of the tendency of an object to keep moving - or how hard it is to stop it moving.
51
What does the momentum of an object depend on?
The momentum of an object depends on its mass and its velocity. Momentum depends on a vector quantity (velocity).
52
How is momentum calculated?
Momentum = mass x velocity Kg m/s Kg m/s p = m x v
53
Momentum and acceleration can be combined to give the equations:
force = mass x change in velocity/ time m(v-u)/t Where v is the final velocity and u is the starting velocity. as mass x velocity is the momentum of an object, this equation can also be written as: force = change in momentum/time or mv-mu/t
54
What happened to the total momentum when moving objects collide and what is the conservation of momentum?
When moving objects collide in the total momentum of both objects is the same before the collision as it is after the collision as long as there are no external forces acting on it. This is the conservation of momentum.
55
What do you need to consider when you add the quantities together?
Remember, momentum is a vector so you need to consider direction when you add the quantities together. If two objects are moving in opposite directions, we give the momentum of one object a positive sign and the other a negative sign.
56
What is the thinking distance?
When a driver sees a problem ahead, their vehicle will travel some distance while the driver reacts to the situation.
57
What is the breaking distance?
The vehicle will then go some distance further while the brakes are working to bring it to a halt.
58
What is the stopping distance?
Stopping distance = thinking distance + braking distance
59
What is a reaction time?
A reaction time is the time between a person detecting a stimulus (such as a flashing light/sound) and their response (such as applying breaks)
60
How can response time be calculated?
Response times can be measured using computers or electric circuits that measure the time between a stimulus and a response.
61
What is the typical reaction time to a visual stimulus?
0.25 seconds.
62
How can reactions to a stimulus be increased? (or thinking distance that results in an increased thinking time when stopping a car)
- alcohol - Drugs - tiered - ill - on the phone - other distractions These all increase reaction time.
63
How can reaction time get decreased?
Caffeine
64
How does friction affect cars stopping?
Car brakes use friction to to slow down cars. If the brakes are worn, they create mess friction and do not slow the vehicle as effectively.
65
What factors can increase breaking distance?
- weather (wet road) - worn out tyres (car in need of an MOT) - loose gravel - flat tyre
66
How does the mass of a vehicle affect the acceleration of it?
If the vehicle has more mass, more force is needed to decelerate it. So if the same amount of friction is used to stop a vehicle, a heavier vehicle will travel further than a lighter one (it has a breaking distance)
67
The force used to accelerate an object transfers what? And what does it depend on?
Transfers energy to it. The amount of energy transferred depends on the size of the force and how far the object moves while the force is pushing it.
68
What is work done?
The energy transferred by a force acting over a distance is called work done.
69
How do you calculate work done?
Work done = force x distance moved in direction of force | (J) (N) (M)
70
What is kinetic energy?
The energy stored in a moving object.
71
What does the amount of kinetic energy depend on?
It depend on the mass of an object and its velocity.
72
What is the equation for kinetic energy?
Kinetic energy = 1/2 x mass x speed squared | (J) (Kg) (m/s squared)
73
What happens to the kinetic energy when a vehicle stored?
When a vehicle stop the kinetic energy is transferred to other energy stores by the braking force. We can use this idea to calculate the braking distance if the vehicle.
74
What energy store does the braking distance if a car depend on?
Kinetic energy and so it depends on the square of its velocity. This means that if the velocity doubles, the braking distance is multiplied by 2 squared which is 4.
75
What is deceleration?
Slowing down if an object. Also known as negative acceleration.
76
What the force needed for any kind for any kind of acceleration depend on?
The size of acceleration and on the mass of the object.
77
What features to modern cars have built into them and why?
Safety features built into help them reduce the force in the occupants in a collision. Crumple zones are built into the front (and sometimes back) of cars.
78
What do crumple zones do?
If the car hits something it takes a little time for this crumpling to happen, so the deceleration if the car is less and the force on the car is also less than if it had a more solid front.
79
What do seatbelts do?
Seatbelts hold the passengers into the car, so the effect of the crumple zones reduces the forces on the passengers as well as the car.
80
What do airbags do?
Air bags increase the time it takes for a persons head to stop on a collision.
81
What does the force of a road Collin depend on and what equation can be used to calculate the force?
Depends on momentum as the car comes to a stop. F = mv-mu/t

Physics (11 decks)

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