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Physics > Dynamics > Flashcards

Dynamics Flashcards

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1
Q

What is mass (kg) described as?

A

The quantity of matter in a body.

Thought of as a measure of a body’s inertia (resistance to acceleration).

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2
Q

What is weight (N) described as ?

A

The force by which the body is gravitationally attracted to the earth, as a product of mass and the acceleration of free fall (N = mass x 9.8)

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3
Q

What is force (N) described as?

A

The agency that tends to change momentum of a body, defined as being proportional to the rate of increase of momentum.

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4
Q

What is Newton’s First law of motion?

A

A body remains in a state of uniform motion or rest, unless acted upon by an external force.

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5
Q

What is Newton’s Second Law of motion?

A

The rate of change of momentum of a body is proportional to the resultant force, that acts in the direction of the force.

Force = mass x acceleration (F = ma)

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6
Q

What is Newton’s Third Law od Dynamics?

A

When one body exerts a force on another body, the second body exerts an equal and opposite force on the first body.

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7
Q

What is linear momentum (p) ?

A

The prodcut of a body’s mass and velocity. (kgms^-1)

p = mv

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8
Q

What is impulse ?

A

A force (F) that acts on a body during a time (t) provides the body with an impulse of Ft.

Ft = force x time interval

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9
Q

What does impulse equal?

A

The momentum change on a body is equal to the impulse provided by the force acting on it.

Impulse = momentum change.

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10
Q

What is the law of Conservation of Momentum ?

A

The total momentum in any given direction before impact is equal to the total momentum in that direction after impact .

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11
Q

What is an elastic collision?

A

In which both conservation of momentum and conservation of kinetic energy is observed.

All kinetic energy of the objects before the collision is still in the form of kinectic energy after.

mv1 = mv’1 + mv’2

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12
Q

What is an inelastic collision?

A

In which part of the kinetic energy is changed to some other form of energy after the collision.

In a perfectly inelastic collision, the bodies stick together and the kinectic energy loss is the maximum possible consistent with momentum conservation.

m1v1 = (m1+m2) x v2.

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13
Q

What are the majority of collisions?

A

Inelastic, being somewhere between elastic and perfectly inelastic.

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14
Q

What is work?

A

The measure of the amount of change that a force produces when it acts on a body.

It may be velocity, position, size or shape.

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15
Q

What is the equation for work?

A

Work = force x displacement.

W = Fs

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16
Q

What is power?

A

The rate at which work is done by a force.

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17
Q

What is the equation for power (watts) ?

A

Power = work done / time

P (watts) = W / t

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18
Q

What is Brake Horsepower?

A

The engine is made to do work on a device known as a dynamometer or brake.

This loads the engine output whilst a reading of the work can be taken.

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19
Q

What is Shaft Horsepower?

A

Similar to BHP except that the measurement is being taken at the output shaft of a turbo-prop engine.

20
Q

What is energy? ( Joules)

A

The property that something has which enables it to do work. The more energy = the more work it can perform.

21
Q

What is potential energy?

A

The energy a body has by virtue of its postion.

PE = w (i.e. m x g) x h

22
Q

What is kinetic energy?

A

The energy a body has by virtue of its motion.

KE = 1/2(mv^2)

23
Q

What is the principle of the conservation of energy?

A

The total amount of energy (KE + PE) which the bodies possess in an isolated system, is constant.

(Frictionless motion only)

24
Q

If the system is not conservative (i.e. there is friction), what is the KE formula?

A

Loss of KE = gain in PE + gain of internal energy.

25
Q

What is centripetal force described as?

A

The force that produces the acceleration of a body travelling with uniform speed in a circular pattern.

26
Q

What is the equation for centripetal force?

A

Fc = mv^2 / r

Towards the centre of the circle.

27
Q

What does centrifugal force exist as?

A

An equal and opposite reaction to centripetal force.

28
Q

What is simple harmonic motion?

A

Periodic motion that occurs when the restoring force on a body, displaced from an equilibirum position, is proportional to the displacement and in the opposite direction.

29
Q

What is restoring force?

A

When an onject is stressed or compressed, a force appears that attempts to return the object to its normal length.

Fr = -ks

where k = force constant and s = displacement.

30
Q

What is elastic potential?

A

As work has to be done by an applied force to stretch or compress an object, the object has elastic potential energy.

PE = 1/2(ks^2)

31
Q

What are the two types of vibration?

A

Free and forced.

32
Q

When do free vibrations occur?

A

Where the total energy of a vibrating system stays constant.

33
Q

What is natural frequency?

A

When a system oscillates without any force applied.

34
Q

When do forced vibrations occur?

A

Where the frequencies of the periodic force build up amplitude, then slow down motion, then build up again etc.

35
Q

What is resonance ?

A

When the force frequency equals the natural frequency.

36
Q

What is damping?

A

A decrease in the amplitude of an oscillation as a result of energy being drained, to overcome resistive forces .

37
Q

What is a result of over/heavy-damping?

A

The system will not oscillate when displaced from its equilibrium and would be slow to return to equilibrium.

38
Q

What is a critically damped system?

A

When a system is displaced and released, it returns to equilibrium without overshooting and in the shortest time possible.

39
Q

What are the two properties that govern a gyro?

A

Rigidity in inertial space and precession.

40
Q

What is the rigidity of a gyro?

A

Even if the location of the gyro changes, the axis of spin will continue to point in the same direction relative to space unless acted upon by an external force.

41
Q

What factors affect the rigidity of a gyro?

A

The mass of the rotating body, the distribution of mass, and its angular velocity.

42
Q

What is gyroscopic procession ?

A

Caused by the applied force being carried in the direction of spin. This results in the torque apparently acting perpendicular to the axis around which the torque was applied.

43
Q

What can unbalanced high speed rotating equipment result in?

A

Noise, component wear, excessive vibration, and shortening of bearing life.

44
Q

What must a body possess to be completely balanced? (2)

A

Static and dynamic balance.

45
Q

When does static balance occur?

A

When there is no resultant rotational force and the centre of gravity is on the axis of rotation.

46
Q

When does dynamic balance occur?

A

When there is no resultant turning moment along the axis.

Physics (7 decks)

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