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Physics > Mechanics > Flashcards

Mechanics Flashcards

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1
Q

Define vector. Give three examples.

A

A vector quantity is a quantity with both magnitude and direction. E.g. Displacement, Velocity, acceleration, force, moment of a force, momentum.

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2
Q

Define scalar quantity. Give three examples.

A

A scalar quantity is a quantity with magnitude but not direction. E.g. Work, energy, power, mass, density, time, temperature.

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3
Q

Define displacement. Define velocity.

A

Displacement is the distance travelled in a particular direction. Measured in metres. Rate of change of displacement.

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4
Q

On a velocity time graph what is the slope of the graph and the area under the graph?

A

Slope: Acceleration
Area: Displacement

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5
Q

Define newton’s first law of motion.

A

A body continues in a state of rest or uniform motion in a straight line unless a resultant external force acts on it.

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6
Q

Define mass.

A

Mass is a measure of a body’s inertia. I.e. it’s reluctance to change velocity

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7
Q

Define friction.

A

Friction is a force that opposes the relative motion of two objects in contact.

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8
Q

Define momentum in words and formula.

A

The momentum of a body is the mass multiplied by the velocity.
p = m x v

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9
Q

Define the unit of force.

A

1N = 1kg accelerated at 1ms-2

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10
Q

Define weight.

A

The weight of a body is the force of gravity acting on the body.

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11
Q

Define newton’s second law of motion.

A

When a resultant external force acts upon the body the rate of change of the momentum of the body is proportional to this force and takes place in the direction of the force.

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12
Q

Define Newton’s third law of motion.

A

For every action there is an equal and opposite reaction. Action and reaction do not happen on the same body.

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13
Q

In the F proportional to a experiment what is the slope of the graph equal to.

A

Mass of the body

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14
Q

State the law of the conservation of momentum.

A

When two or more bodies interact in a closed system, the total momentum of the bodies before the interaction equals the total momentum of the bodies after the interaction.

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15
Q

Define pressure. Give formula.

A

Pressure is force per unit area. Measured in pascal (Pa)
p = F/A

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16
Q

Define pressure in a fluid. Formula only.

A

p = density x g x h

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17
Q

Why is pressure a scalar quantity?

A

It acts in all directions.

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18
Q

Give the formula for density.

A

Density = mass/volume

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19
Q

State archimedes’ principle.

A

When an object is partially or fully immersed in a fluid it will experience an upthrust equal in magnitude to the weight of the fluid displaced

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20
Q

Define the law of floatation.

A

When an object floats the weight of the object in air equals the weight of the fluid displaced.

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21
Q

What instrument is used to measure the density of a liquid?

A

Hydrometer.

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22
Q

State Boyle’s Law.

A

For a fixed mass of gas at a fixed temperature the pressure of the gas is inversely proportional to the volume of the gas.

23
Q

Define moment of a force. Formula only but give unit. Define moment of a force when angle is not at 90 degrees.

A

M = F x d. Newton metre.
M = Moment of a force; F = Force; d = perpendicular distance from line of action of force to the axis.

M = Fxdxsin (pieta)

24
Q

Define moment of a couple. Formula only but give unit.

A

T = F x d. Unit is Newton Meter
T=moment of a couple/Torque; F=Force; d=perpendicular distance between lines of action.

25
Q

State the two conditions that must be met for an object to be in equilibrium.

A

The vector sum of the forces in any direction on the body is zero.
The sum of the moment of the forces about any point on the body is zero.

26
Q

What is terminal velocity?

A

When the up forces equal the down forces and the object stops accelerating.

27
Q

Formula to calculate an angle in radians.

A

Angle in radians = arc length/radius length = s/r

28
Q

Define angular velocity with formula.

A

w = theta / t (w = angular velocity, theta = change in angular displacement, t = time taken for change)

29
Q

Define Periodic Time.

A

The periodic time or more simply the period is the time taken to complete one full circular motion.

30
Q

Why does an object accelerate when moving in a circle with a constant velocity?

A

It is constantly changing direction.

31
Q

Define centripetal acceleration.

A

Centripetal acceleration is the acceleration acting towards the centre of a circle keeping an object in uniform circular motion.

32
Q

Define centripetal force.

A

Centripetal force is the force acting towards the centre of the circle keeping an object in uniform circular motion.

33
Q

Define Newton’s Law of Universal Gravitation.

A

Any two point masses in the universe attract each other with a force that is directly proportional to the product of the masses and inversely proportional to the square of the distance between the point masses.

34
Q

Define geostationary satellite.

A

Geostationary satellites give the illusion of being stationary above a particular point on the earth. To an observer on the earth it seems that the satellite is always in the same place.

35
Q

State three conditions for a satellite to be geostationary.

A
  1. Orbit the earth in the equatorial plane.
  2. Have the same rotational period as the earth.
  3. Move in the same direction as the rotation of the earth.
36
Q

What are geostationary satellites used for?

A

Geostationary satellites are used for communication.

37
Q

State two mathematical expressions used to get the speed of a satellite.

A

v = Root (GM / r)
Or
v = 2 兀 x R / T

38
Q

Define Simple Harmonic Motion.

A

Simple Harmonic Motion is the motion of an object whose acceleration is proportional to its displacement from a fixed point. The direction of acceleration is opposite to the direction of displacement.

39
Q

Define Hooke’s Law.

A

If an object is stretched or compressed the restoring force is directly proportional to the displacement if you stay within the elastic limit of the object.

40
Q

What three attributes of acceleration occur when a system obeys Hooke’s Law?

A

The acceleration will consist of:
-A minus sign
-A constant
-A displacement

41
Q

How can the length of a pendulum be accurately measured?

A

A split cork enables this as the length of the pendulum is from the point the string leaves the split cork to the centre of gravity of the bob.

42
Q

Define force.

A

Force is what causes acceleration.

43
Q

What is meant by the centre of gravity of a body?

A

The point of a body where its’ weight appears to act.

44
Q

If the acceleration due to gravity on the ISS is 8.63ms-2 why do the astronauts experience weightlessness.

A

The ISS is in freefall towards the Earth.

45
Q

Why does bobble turn always right itself when knocked over?

A

Toy is non-vertical and has a turning moment about fulcrum.

46
Q

Other than a mass at the end of a spring. Give two examples of Hooke’s law.

A

Pendulum. Vibrating tuning fork.

47
Q

How can a rotating object be in equilibrium?

A

Constant angular velocity.

48
Q

Why is there no atmosphere on the moon?

A

Gravitational force too weak to sustain atmosphere.

49
Q

Explain why satellites remain in orbit and don’t fall to Earth.

A

Horizontal velocity.

50
Q

Why is it easier to lift something with a longer lever?

A

Greater Torque

51
Q

When does a simple pendulum execute S.H.M.? Why does a body move with S.H.M.?

A

When oscillating at a small angle.

Acceleration proportional to displacement.

52
Q

Tidal power and wave power are different explain why?

A

Tidal power is from moon.
Wave from wind from the sun

53
Q

Formula for tension in a cable lifting a heavy block.

A

T - mg = ma

T is Tension/Force
m is mass of block
a = acceleration of block upward
g = acceleration due to gravity

54
Q

When an object moves with circular motion attached to string? Formula for tension on string.

A

T = centripetal force - force of gravity

Physics (16 decks)

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