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A Level Physics > 3 Forces and Motion > Flashcards

3 Forces and Motion Flashcards

1
Q

Instantaneous speed

A

The speed of the car over a very short interval of time

Found by drawing tangent to distance-time graph at that time

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2
Q

Average velocity graph

A

Change in displacement/ time taken

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3
Q

Average acceleration equation

A

Change in velocity/ change in time

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4
Q

Acceleration from graph

A

Gradient of velocity-time graph

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5
Q

Stopping distance

A

Thinking distance + braking distance

Total distance travelled from when the driver first sees a reason to stop, to when the vehicle stops

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6
Q

Thinking distance

A

Distance travelled between the moment when you first see a reason to stop, to the moment when you use the brake

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7
Q

Braking distance

A

The distance travelled from the time the brake is applied until the vehicle stops

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8
Q

Thinking distance equation

A

Speed x reaction time

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9
Q

Free fall

A

When an object is accelerating under gravity, with no other force acting on it

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10
Q

Determining g in lab experiments

A

Electromagnet and trapdoor
Light gates
Taking photos of dropped ball next to metre rule

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11
Q

The moment of a force

A

The turning effect of a force about some axis or point

Moment= force x perpendicular distance of the line of action of force from the axis or point of rotation

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12
Q

Perpendicular distance

A

Use the perpendicular distance in calculations involving moments, not just the distance from force to pivot

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13
Q

The principle of moments

A

For a body in rotational equilibrium, the sum of the anti-clockwise moments about any point is equal to the sum of the clockwise moments about the same point

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14
Q

Torque of a couple

A

The moment of a couple is known as a torque. The torque of a couple is defined as
torque of the couple = one of the forces X perpendicular separation between the forces
=Fd

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15
Q

Density

A

Mass per unit volume

Kgm-3

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16
Q

Pressure

A

Normal force exerted per unit cross sectional area

Nm-2 or Pa

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17
Q

Pressure in liquids

A

p=hpg
Height x density x acceleration of free fall
Pressure at base is equal to the weight of column divided by cross sectional area

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18
Q

Archimedes’ principle

A

The upthrust exerted on a body immersed in a fluid is equal to the weight of the fluid that the body displaces

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19
Q

When will an object sink

A

If the upthrust is less than the weight of the object

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20
Q

Floating objects

A

The upthrust equals the eight of the objects

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21
Q

Work done

A

Energy transferred

Nm or J

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22
Q

Work done at angle to motion

A

Work done W= (F cos(theta)) * x

W=Fxcos()

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23
Q

Energy

A

The capacity for doing work
Scalar
Joules

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24
Q

Forms of energy

A 
Kinetic energy
Gravitational potential 
Chemical
Elastic potential 
Electrical potential 
Nuclear
Radiant/electromagnetic 
Sound
Thermal
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25
Q

The principle of conservation of energy

A

The total energy of a closed system remains constant: energy can never be created or destroyed, but it can be transferred from one form to another

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26
Q

Kinetic energy

A

Energy associated with an object as a result of its motion

Kinetic energy = 0.5 X mass X velocity2

27
Q

Gravitational potential energy

A

The capacity for doing work as a result of an object’s position in a gravitational field
Gravitational potential energy = mass X gravitational field strength X height

28
Q

Power

A

The rate of work done

Js-1 or W

29
Q

Tensile forces

A

Forces that produce extension

30
Q

Compressive forces

A

Forces that shorten an object

31
Q

Hooke’s law

A

The extension of the spring is directly proportional to the force applied. This is true as long as the elastic limit of the spring is not exceeded

32
Q

Elastic deformation

A

Means that the spring will return to its original lights when the force is removed

33
Q

Plastic deformation

A

Permanent structural changes to the spring occur and it does not return to its original length when the force is removed

34
Q

Force constant K

A

For a spring obeying hooke’s law, the applied force F is directly proportional to the extension x.Therefore F =kx

35
Q

What shows work done on a force – extension graph

A

Area under the graph

36
Q

Loading and unloading metal wire

A

Follows Hooke’s law until the elastic limit of the wire
Beyond the elastic limit it is parallel to the loading graph but not identical to it
The wire is permanently extended after the force is removed- it’s longer than it was at the start

37
Q

Loading and unloading rubber

A

Don’t obey Hooke’s law
Rubber band will return to its original length after the force is removed- elastic deformation
The loading and unloading graphs are both curved and are different
Hysteresis loop

38
Q

Unloading and loading polythene

A

Doesn’t obey Hooke’s law

Suffer plastic deformation under little force

39
Q

Tensile stress

A

The force applied per unit cross sectional area of the wire

Sigma is symbol for tensile stress

40
Q

Tensile strain

A 
The fractional change in the original length of the wire
Curvy E (epsilon) is tensile strain
41
Q

Ultimate tensile strength

A

The maximum stress that a material can withstand when being stretch before it breaks
Beyond this point the material may become longer thinner at its weakest point, a process called necking

42
Q

Breaking point

A

Where the material eventually snaps from the stress it’s put under

43
Q

Breaking strength

A

The stress value at the point of fracture

44
Q

Strong material

A

One with a high ultimate tensile strength

45
Q

Young modulus

A

Tensile stress/ tensile strain
The ratio of stress to strain for a particular material
Gradient of stress-strain graph
Nm-2 or Pa

46
Q

Stress-strain graph for brittle materials

A

Straight line. 2 arrows pointing into each other

Ultimate tensile strength is same as breaking strength

47
Q

Polymeric materials

A

Materials that consist of long molecular chains

Polythene and rubber

48
Q

Stress-strain graph for rubber

A

Marble swirl shape?????

Clockwise arrows

49
Q

Stress-strain graph for polythene

A

Straight line then levels off

50
Q

Newton’s first law of motion

A

An object will remain at rest or continue to move with constant velocity unless acted upon by a resultant force

51
Q

Newton’s third law of motion

A

When two objects interact, they exert equal and opposite forces on each other

52
Q

Types of interaction

A

All interactions can be explained in terms of four fundamental forces- gravitational, electromagnetic, strong nuclear and weak nuclear.
The two nuclear forces have a very short range and so very little impact on things we observe in daily life.
When you push your hands together, the contact force you feel is due to the electrostatic repulsive forces between the electron clouds around the atomic nuclei in your hands

53
Q

Momentum

A

Momentum= mass x velocity

Kg m s-1

54
Q

Conservation of momentum principle

A

For a system of interacting objects, the total momentum in a specified direction remains constant, as long as no external forces act on the system

55
Q

Total momentum before collision=

A

Total momentum after collision

56
Q

Zero momentum example- gun

A

A gun recoils when a bullet is fired. The total momentum of this system remains the same and is equal to zero. The momentum of the gun and the momentum of the bullet have the same magnitude but act in opposite directions

57
Q

Two types of collisions

A

Perfectly elastic

Inelastic

58
Q

Summary of perfectly elastic collision

A

Momentum- conserved
Total energy- conserved
Total kinetic energy- conserved

59
Q

Summary of inelastic collision

A

Momentum- conserved
Total energy- conserved
Total kinetic energy- not conserved

60
Q

Newton’s second law of motion

A 
The net (resultant) force acting on an object is directly proportional to the rate of change of its momentum, and is in the same direction 
Net Force= change in momentum/time
Also F=ma
61
Q

Why is momentum conserved in collisions?

A

The net force on the objects in a closed system is zero. According to Newton’s second law change in momentum/time=0. The change in momentum of both objects must be zero; therefore, the total momentum of the objects doesn’t change
Momentum is always conserved

62
Q

Impulse of a Force

A

Forces accelerating or decelerating an object usually change over time e.g. kicking a ball. This type of motion can be analysed using the idea of impulse
Impulse of a Force= change in momentum
=Ft

63
Q

Unit of impulse

A

Ns

Kg m s-1

64
Q

Area under force-time graphs

A

Impulse

Area=Ft

A Level Physics (15 decks)

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