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Physics > Module 3 > Flashcards

Module 3 Flashcards

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1
Q

When can the SUVAT equations be used?

A

When there is a constant acceleration.

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2
Q

What are the SUVAT equations?

A

v=u+at
s=ut+1/2at^2
s=1/2(u+v)t
v^2=u^2+2as

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3
Q

What is the stopping distance?

A

The total distance travelled from when the driver first sees a reason to stop, to when the vehicle stops.

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4
Q

What is thinking distance?

A

The distance travelled between the moment when you first see a reason to stop, to the moment when you use the break.

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5
Q

What is breaking distance?

A

The distance travelled from the time the break is applied until the vehicle stops.

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6
Q

How can you determine g?

A

Electromagnetic trapdoor:
- an electromagnetic holds a small steel ball above a trapdoor
- when the current is switched off, a timer is triggered and the ball falls
- when the ball hits the trapdoor, the electrical contact is broken and the timer stops
- g is calculated from the height of the fall and time taken.
Light gates:
- two light beams, one above the other, are connected to a timer
- when the ball falls through the first beam, the light interrupts and the timer is started
- the ball falls through the second beam the timer stops.

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7
Q

What is a Newton?

A

The force required to accelerate a 1kg mass by 1ms^-2

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8
Q

What is the centre of mass of an object?

A

A point through which any externally applied force produces straight-line motion but no rotation. It is an imaginary point where the weight of an object appears to act.

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9
Q

How can you find the centre of gravity?

A

A freely suspended object will come to rest with its centre of gravity vertically below the point of suspension. This means that you can use a plumbline to find it. Suspend the object in different orientations, and mark the line of the plumbline with a pencil. The centre of gravity will be the point where the pencil lines intersect.

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10
Q

How do you represent forces on a free body diagram?

A
  • each force vector is represented by an arrow labelled with the force it represents
  • each arrow is drawn to the same scale (the longer the arrow, the greater the force)
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11
Q

What is drag?

A

A frictional force which opposes the motion of the object.

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12
Q

When will an object reach terminal velocity?

A

When the drag force on the object is equal and opposite to the weight.

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13
Q

How can you investigate the motion of an object falling through a fluid?

A
  • set up equipment with the fluid in a tube, a motion sensor connected to a laptop, and the falling object attached to a thread with a light ball on the other end, on the other side of a pulley
  • drop the object through the cylinder of liquid. This will pull the light ball vertically upwards.
  • the motion of this ball is identical to that of the object falling through the fluid, but can be picked up by the motion sensor.
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14
Q

What is 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 the force from the point of rotation.
M=Fx

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15
Q

What is the principle of moments?

A

For a body in rotational equilibrium, the sum of the anticlockwise moments about any point is equal to the sum of the clockwise moments about that same point.

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16
Q

What is a couple?

A

A pair of forces that cause rotational motion without translational motion. They are equal and opposite and are parallel along different lines.

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17
Q

What is torque?

A

The moment of a couple.
Calculated by one of the forces times the perpendicular separation between the forces.

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18
Q

What is the density of a substance?

A

Its mass per unit volume.

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19
Q

How can you determine density?

A

Find the mass using a balance. Find the volume of a liquid using a measuring cylinder, a regular shaped objects from measurements made with a ruler, and irregular shaped objects can be determined by how much of a fluid they displace.

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20
Q

What is pressure?

A

The normal force exerted per unit cross-sectional area.

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21
Q

How do you calculate the pressure exerted by a vertical column of liquid?

A

P=hpg
Derived from W= mass of column x g

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22
Q

How do you calculate upthrust?

A

force at the top surface = hpgA
force at the bottom surface = (h+x)pgA
resultant upward force = (h+x)pgA-hpgA
=Axpg

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23
Q

What is Archimedes’ principle?

A

The upthrust exerted on a body immersed in a fluid, whether partially or fully submerged, is equal to the weight of the fluid displaced.

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24
Q

What is work done?

A

force x distance moved in the direction of the force.
It is the same as energy transferred.

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25
Q

What is a Joule?

A

The work done when a force of 1N moves its point of application 1 m in the direction of the force.

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26
Q

What is energy?

A

The capacity to do work.

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27
Q

What is kinetic energy?

A

Energy due to the motion of an object with mass.

28
Q

What is gravitational potential energy?

A

Energy of an object due to its position in a gravitational field.

29
Q

What is chemical energy?

A

Energy contained within the chemical bonds between atoms.

30
Q

What is elastic potential energy?

A

Energy stored in an object as the result of a reversible change in its shape.

31
Q

What is electrical potential energy?

A

Energy of electrical charges due to their position in an electric field.

32
Q

What is nuclear energy?

A

Energy within the nuclei of atoms.

33
Q

What is electromagnetic (radiant) energy?

A

Energy associated with all electromagnetic waves, stored within the oscillating electric and magnetic fields.

34
Q

What is internal energy (heat or thermal)?

A

The sum of the randomly distributed potential and kinetic energies of atoms in a system.

35
Q

What is the principle of the 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.

36
Q

What is power?

A

The rate of work done.
P=W/t

37
Q

How do you calculate efficiency?

A

(useful output energy)/(total input energy) x 100

38
Q

What are tensile forces?

A

Forces that produce extension.

39
Q

What are compressive forces?

A

Forces that compress an object.

40
Q

When does tensile deformation occur?

A

When tensile forces are exerted.

41
Q

When does compressive deformation occur?

A

When compressive forces are exerted.

42
Q

When does the force-extension graph look like?

A

A straight line from the origin up to the elastic limit.

43
Q

What is elastic deformation?

A

When a material will return to its original shape/size when the force is removed.

44
Q

When does plastic deformation occur?

A

When permanent structural changes to the material occur and it does not return to its original shape/size once the force is removed.

45
Q

What is Hooke’s law

A

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

46
Q

What is the force constant a measurement of?

A

Stiffness

47
Q

How can you investigate Hooke’s law?

A
  • attach a spring at one end using a clamp, boss, and clamp stand
  • set up a meter ruler close to the spring
  • suspend masses from the spring and, as you add each one, record the total mass added and the length of the spring.
48
Q

What does the loading and unloading curve look like for metal wire?

A

The loading graph follows Hooke’s law until the elastic liming of the wire. The unloading graph will be identical for forces less than the elastic limit.
Beyond the elastic limit the unloading graph is parallel to the loading graph but not identical to it.
The wire is permanently extended after the force is removed.

49
Q

What does the loading and unloading curve look like for rubber?

A

Rubber does not obey Hooke’s law. The rubber band will return to its original length after the force is removed, but the loading and unlading graphs are both curved and are different.
The loop formed is called a hysteresis loop. The area inside a hysteresis loop is the thermal energy released when the material is loaded and unloaded. This is because it requires more work to stretch rubber than is done when its extension decreases again.

50
Q

What does the loading and unlading curve look like for polythene?

A

Polythene does not obey Hooke’s law. Thin strips of polythene are very easy to stretch and they suffer plastic deformation under little force. The loading curve is the same as for rubber, but the unloading curve is a straight line down, with a gradient slightly towards the origin.

51
Q

What is tensile stress?

A

The force applied per unit cross-sectional area of the wire.
sigma=F/A
It has the unit pascals.

52
Q

What is tensile strain?

A

The fractional change in the original length of the wire.
epsilon = extension/original length = x/L
It has no units.

53
Q

What is a ductile material?

A

A material that can be easily drawn in to a wire or hammered into thin sheets.

54
Q

What are yield points?

A

Points where the material extends rapidly.

55
Q

What is ultimate tensile strength?

A

The maximum stress that a material can withstand when being stretched before it breaks

56
Q

What is a materials breaking strength?

A

The stress value at the point of fracture. After the UTS the material may become longer and thinner at its weakest point, known as necking. The material will eventually snap at this point.

57
Q

What is the Young modulus?

A

The ratio of stress to strain for a particular material within the limit of proportionality.
E=sigma/epsilon

58
Q

How can you determine a wires Young modulus?

A
  • set up a clamp holding a length of wire across a table, with a pully and masses at the other end of the table. Use a piece of tape as a marker and put a ruler on the table below this marker
  • the diameter of the wire can be measured using a micrometre, and this can be used to calculate CSA
  • after applying each mass, the extension can be calculated using the marker and the ruler
  • plot a stress-strain graph and find the gradient.
59
Q

What is a brittle material?

A

A material that shows elastic behaviour up to its breaking point, without plastic deformation. This means that the UTS is the same as the breaking strength.

60
Q

What are polymeric materials?

A

Materials that consist of long molecular chains. They behave differently depending on their molecular structure and temperature.

61
Q

What is Newton’s first law?

A

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

62
Q

What is Newton’s third law?

A

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

63
Q

What is the principle of conservation of momentum?

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.

64
Q

What quantities are conserved in a perfectly elastic collision?

A

Momentum, Total energy, Total kinetic energy.

65
Q

What quantities are conserved in an inelastic collision?

A

Momentum, Total energy.

66
Q

What is Newton’s second law?

A

The resultant force acting on an object is directly proportional to the rate of change of its momentum, and is in the same direction.

Physics (6 decks)

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