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Dynamics and Forces Flashcards

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1
Q

What is Newton’s first law of motion?

A

Law of inertia: a body remains at rest or continues to move in a straight line with a uniform velocity unless a net external force acts on it.

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2
Q

What is Newton’s second law of motion?

A

The rate of change of momentum of a body is proportional to the net force producing it, and it takes place in the direction of this net force.

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3
Q

What is Newton’s third law of motion?

A

The forces of a action and reaction between interacting bodies are equal in magnitude, opposite in direction and act on different bodies.

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4
Q

What is the difference between mass and weight?

A

Mass is a measure of inertia in a body while weight is the effect of a gravitational field on a mass.

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5
Q

Relate weight, mass and acceleration of free fall.

A

W=mg

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6
Q

What is linear momentum of a body?

A

It is the product of its mass and velocity.

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7
Q

What is force?

A

It is the rate of change of momentum of the body acted upon (N2L)

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8
Q

What is impulse? (J)

A

Product of the force and time interval which the force acts.

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9
Q

The impulse of a variable force is equivalent to ____.

A

The impulse of a constant average force in the same time interval.

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10
Q

What is force?

A

It is the rate of change of momentum.

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11
Q

Acceleration and net force are always ____.

A

In the same direction.

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12
Q

Under Newton’s third law, the equal but opposite forces act on _____.

A

Different bodies.

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13
Q

Weight does not have a _____.

A

Horizontal component.

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14
Q

State the principle of conservation of linear momentum.

A

The total linear momentum of an isolated system(no net external force) remains constant.

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15
Q

Total momentum before collision = total momentum after collision
Thus, rearrange the equation to obtain the changes in momentum of each mass.

A

m1u1+m2u2=m1v1+m2v2

m1(v1-u1)=-m2(v2-u2)

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16
Q

In all collisions, momentum is conserved but kinetic energy is only conserved in _____.

A

Elastic collisions.

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17
Q

In an elastic collision, relative velocity of approach= ?

A

-relative velocity of separation

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18
Q

In elastic collisions, if the bodies have the same mass, their velocities are _____.

A

Exchanged upon collision.

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19
Q

For in elastic collisions compare the relative speeds of approach and separation.

A

Approach > separation assuming no explosive separation.

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20
Q

If two colliding bodies coalesce after impact, why is the collision in elastic?

A

There is zero separation. Which means the relative speed of separation is 0, which is less than approaching speed.

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21
Q

What is an explosive separation?

A

It is when two or more bodies separate due to a rapid release of energy.
Total momentum before the separation has to be 0.

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22
Q

What is the ration of kinetic energies of bodies undergoing explosive separation?

A

v1/v2 and hence m2/m1 since the momentum after the separation is equal.

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23
Q

How is the force derived when mass is varying but velocity is constant?

A

F=vδm/δt.

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24
Q

When is Newton’s 2nd law applied?

A

When there is a change in momentum ie change in mass or velocity.

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25
Q

What is Hooke’s law?

A

Within elastic limit, the magnitude of tension in an elastic body is directly proportional to its extension.

26
Q

What is the equation for Hooke’s law?

A

T=-kx

27
Q

Tension of a spring is always _____ in direction to the extension.

A

Opposite.

28
Q

For a given elastic material, spring constant k is _____ to cross sectional area A and _____ to its natural length lo.

A

Directly proportional, inversely proportional.

29
Q

The net force on a mass suspended from a light spring at equilibrium is _____.

A

Zero.

30
Q

What is a force field?

A

If is a region of space within which force is experienced.

31
Q

A uniform field is represented by _____ lines.

A

Parallel.

32
Q

What is gravitational field strength g at a point? State the equation for gravitational force.

A

It is the gravitational force per unit mass acting on a small stationary test mass placed at that point.
F=mg

33
Q

What is electric field strength at a point?

A

It is the force per unit positive charge acting on a small stationary test charge placed at that point.
F=QE

34
Q

What is the magnitude of magnetic force in a conductor of length l carting a current I in a magnetic field with magnetic field strength B?

A

F=BIlsinθ where θ is the angle to the field.

35
Q

What is the magnitude of magnetic force on a charge Q moving at velocity v at an angle θ to the magnetic field of field strength B?

A

F=BQvsinθ

36
Q

What is pressure?

A

It is the force per unit area.

37
Q

What is density?

A

Mass per unit volume.

38
Q

What is the pressure p at depth h of a fluid of density ρ?

A

p=hρg

39
Q

Derive p=hρg from p=F/A.

A

p=F/A=mg/A=ρVg/A=hρg

40
Q

What is the actual pressure in a fluid?

A

Sum of pressure due to the fluid and any pressure subjected on the fluid.

41
Q

What is up thrust?

A

It is the upward force exerted by a fluid on a body when it is partially or fully immersed in the fluid.

42
Q

State Archimedes’ principle.

A

When a body is immersed in a fluid, it experiences and up thrust equal to in magnitude to the weight of fluid displaced.

43
Q

Upthrust acts through the _____.

A

Center of gravity of the fluid before it was displaced and is always upwards.

44
Q

How does up thrust arise?

A

Pressure in a fluid increases with depth so the pressure on the lower surface is greater than on the upper surfaces, resulting in a net upward force.

45
Q

If an object floats while partially immersed in a fluid, weight of floating body= ?

A

Weight of fluid displaced.

46
Q

What are the directions of frictional force and normal contact forces?

A

Normal force: perpendicular to Surface.

Friction: parallel to surface, resisting the motion between Teo solid surfaces.

47
Q

What are viscous forces?

A

They are forces in a fluid that resist the relative motion of a body through the fluid.

48
Q

What is the difference between friction and viscous forces?

A

Viscous forces are 0 when relative velocity is 0 while there is always a magnitude of static friction.

49
Q

If Teo or more forces acting on a point are in equilibrium, the vector sum of all forces must be _____.

A

Zero.

50
Q

Geometrically, when vectors representing the forces are connected head-to-tail, the final point of the last vector _____ of the first vector.

A

must be the initial point

51
Q

What is center of gravity?

A

It is the point at which the whole weight of the body appears to act.

52
Q

What is the moment of a force?

A

It is the product if the force and the perpendicular distance between the line of action and the pivot point.

53
Q

What is a couple?

A

It is a pair of forces, equal in magnitude but opposite in direction and so fends go produce rotation only.

54
Q

What is a torque?

A

It is the product of one of the forces and the perpendicular distance between the lines of action.

55
Q

The torque is _____ of the position of the axis of rotation.

A

Independent.

56
Q

What is the difference between torque and moment?

A

Moment refers to the turning effect of a force while torque refers to turning effect without translational effect.

57
Q

What are the possible directions of moment and torque and their axes of rotation?

A

Moment: clockwise and anti clockwise.
Axes: determined using right hand grip rule.

58
Q

A body is in equilibrium if _____.

A

Σall forces=0 and Σall moments about any point = 0.

59
Q

What is the principle of moments?

A

Σclockwise moments=Σanti-clockwise moments about the same point.

60
Q

If only three Non-parallel Coplanar forces maintain a body in equilibrium, their lines of action must be concurrent. Explain what is meant by concurrent.

A

They all must pass through one point.

61
Q

For a body placed on a surface to be in equilibrium, the line of action of its weight must pass within the _____.

A

Contact area.

Physics (12 decks)

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