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Physics > 3.4 Mechanics and materials > Flashcards

3.4 Mechanics and materials Flashcards

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1
Q

What is the definition of a newton?

A

The force needed to give a 1kg mass an acceleration of 1ms^-1.

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2
Q

What is the cause of acceleration in terms of forces?

A

Unbalanced forces that produce a resultant force.

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3
Q

What is terminal velocity?

A

Maximum velocity reached by an object falling through a fluid where weight = drag. So, there’s no acceleration.

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4
Q

How do you calculate the distance if work done and force aren’t parallel?

A

scosx. This figures out displacement in the direction of work done.

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5
Q

What is the relationship between energy transferred and work done?

A

They are the same.

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6
Q

What is the area under a force- displacement graph equal to?

A

Work done

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7
Q

How do you calculate efficiency?

A

Useful output power/ input power

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8
Q

What happens when an object is lifted?

A

Work done is transferred to the gravitational potential store of the object.
The force required is equal to the weight of the object.

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9
Q

Why is work done not equal to energy transferred sometimes?

A

Some work has been done against frictional forces, energy is transferred to thermal energy in the surroundings.

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10
Q

What is the principle of conservation of energy?

A

Energy can’t be created or destroyed, only transferred.
So, in a closed system, energy remains constant.

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11
Q

What is power?

A

The rate at which energy is transferred.

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12
Q

What is the definition of momentum?

A

The product of mass and velocity.

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13
Q

What is Newton’s first law?

A

A body will remain at rest or continue to move at a constant velocity unless acted upon by an external force.

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14
Q

What is Newton’s second law?

A

The acceleration of an object is proportional to the resultant force acting on it and inversely proportional to the mass. (F=ma)

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15
Q

What is Newton’s third law?

A

If object A exerts a force on object B, then object B exerts an equal in magnitude and opposite in direction force on object A. (Forces come in Newton pairs)

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16
Q

What is the principle of conservation of momentum?

A

In a closed system, total momentum before and interaction = total momentum after interaction. (Interactions meaning collisions or explosions)

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17
Q

What is a perfectly elastic collision?

A

A collision in which kinetic energy is conserved.

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18
Q

What is an inelastic collision?

A

Some kinetic energy isn’t conserved. Some is lost as heat to the surroundings.

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19
Q

What is impulse?

A

The change in momentum. Impulse=FΔt. It can be calculated from the area under a force-time graph. So, FΔt =Δmv or FΔt=mΔv if mass is constant.

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20
Q

How do you figure out the resultant force of 2 perpendicular vectors?

A

Draw all the forces tip to tail and then calculate the magnitude and direction using trigonometry.

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21
Q

How do you calculate the horizontal and vertical components of a force?

A

For the side adjacent to the angle, do Force*cosA

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22
Q

What will the free body diagram for an object in equilibrium look like?

A

It will form a closed triangle.

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23
Q

How do you calculate the friction and reaction of the inclined plane?

A

Calculate the vertical and horizontal components of the weight using the angle between the horizontal and the plane.

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24
Q

What type of force is a moment?

A

It is a vector. The direction can be either clockwise or anticlockwise.

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25
Q

What is the definition of a moment?

A

force × perpendicular distance between the lines of action of the forces.

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26
Q

What is the principle of moments?

A

For an object in rotational equilibrium,
Total sum of clockwise moments= Total sum of anticlockwise moments

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27
Q

How do we calculate the moment of a force from a diagram where the force isn’t long enough to find the perpendicular to the pivot?

A

Moment= d(fcosx) This is basically finding the vertical component of the force. And then substituting it into the equation m=fd

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28
Q

What is a couple of forces?

A

A pair of equal and opposite coplanar forces separated by a perpendicular distance.

29
Q

What is the moment of a couple?

A

force x perpendicular distance between the lines of action of the forces.

30
Q

What is the centre of mass?

A

The point through which a single force on the body has no turning effect. The point at which the weight appears to act.

31
Q

What is the definition of displacement?

A

Distance in a given direction.

32
Q

What is the definition of velocity?

A

A change of displacement per unit time.

33
Q

What is acceleration?

A

Change of velocity per unit time.

34
Q

What is uniform acceleration?

A

The velocity of an object moving along a straight line changes at a constant rate.

35
Q

What does the gradient tell us on a velocity-time graph?

A

The acceleration

36
Q

Review acceleration-time, distance-time and velocity-time graphs for a bouncing ball.

A
37
Q

How are we able to calculate the time taken for an object thrown upwards to come back down?

A

Horizontal and vertical motion are independent of each other, other than the fact that they both last for the same time. Horizontal motion has a constant velocity and vertical motion has the constant acceleration of 9.81.

38
Q

How do you calculate the range of an object thrown at an angle?

A
  • Split the launch velocity into its components.
    • Then use SUVAT to calculate the time required to reach the highest point and double this value for total time of flight.
    • Using the horizontal component of launch velocity and time, you can calculate the range.
39
Q

What is the effect of air resistance on the projectile?

A

The range is shorter.
The entire trajectory is below the original.
The initial launch angle remains the same.

40
Q

Explain why an inclined plane rather than freefall would produce more valid results in the freefall experiment?

A

Freefall is too quick and there is no accurate measuring method.

41
Q

What is Hooke’s law?

A

A spring where extension is directly proportional to the force applied.

42
Q

What is elastic potential energy?

A

Energy stored in an elastic material.

43
Q

What happens to the spring constant when a force is applied to 2 identical springs in series?

A

The spring constant is halved.

44
Q

What happens to the spring constant when a force is applied to 2 identical springs in parallel?

A

The spring constant is double that of a single spring.

45
Q

What is stress?

A

Force per unit (cross-sectional) area

46
Q

What is strain?

A

A measure of how much an object has extended per unit of length.

47
Q

What is the equation used to calculate strain?

A

(Extension) / (original length) * 100

48
Q

What is young modulus?

A

It a property of a material which is a measure of stiffness. The higher the young modulus, the more force is required to deform.

49
Q

What is the elastic limit?

A

If you add more load to an object beyond this point, it will plastically deform.

50
Q

What is elastic deformation?

A

The material returns to its original shape and size once the forces are removed.

51
Q

What is plastic deformation?

A

The material doesn’t return to its original shape and size once the forces are removed. It is permanently deformed.

52
Q

What is the spring constant?

A

A measure of stiffness.

53
Q

What is the relationship between work done and elastic strain energy?

A

Before the elastic limit is reached. all this work done in stretching is stored as elastic strain energy in the material.

54
Q

What is breaking stress?

A

The effect of stress is pulling the atoms apart. Breaking stress is when the atoms are completely separated and the material breaks.

55
Q

What is ultimate tensile stress?

A

The maximum stress a material can withstand before fracturing.

56
Q

What is the equation for elastic strain energy?

A

1/2 Fe

57
Q

What is a ductile material?

A

It undergoes a lot of plastic deformation before fracture. E.g copper

58
Q

What is a brittle material?

A

A material that undergoes little to no plastic deformation before fracture.e.g glass, ceramic

59
Q

Rifle B is fired and the bullet emerges with a smaller horizontal velocity that the bullet from rifle A.
Explain why the horizontal distance travelled by bullet B will be less that bullet A.

A

Their vertical motion is independent of their horizontal motion.
Bullets A and B will be in the air for the same time.
(Horizontal acceleration is zero and thus horizontal) distance is proportional to horizontal speed

60
Q

In practice, why is range shorter than calculated?

A

There is air resistance
Which causes horizontal deceleration

61
Q

An apple and a leaf fall from a tree at the same height and time. Explain why the apple hits the ground first.

A

air resistance depends on shape
air resistance less significant (1) air resistance less, therefore greater velocity
[or average velocity greater or accelerates for longer]

62
Q

What is the equation for the young modulus?

A

(Tensile stress)/ (tensile strain)

63
Q

What is lift?

A

Lift is an upward force due to the collisions with air particles on the underside of the wing.
(The wing of a plane pushes air particles downward as it flies forward.As a result of this downward force on the air particles, there is an equal and opposite upward force on the wing.)

64
Q

What increases the drag on an object?

A

Increased surface area
Less streamlined
Increase speed

65
Q

What is the definition for equilibrium?

A

Net / resultant force on an object is zero.
Sum of the clockwise moments about a point equals the sum of the anticlockwise moments about a point.

66
Q

What is the definition of a joule?

A

Energy transferred when 1 newton is applied over 1 metre.

67
Q

What is the definition of a watt?

A

When 1 joule is transferred in 1 second.

68
Q

What is the effect of speed on air resistance?

A

As speed increases, air resistance increases.

Physics (7 decks)

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