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Physics > Forces in Action > Flashcards

Forces in Action Flashcards

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1
Q

If you apply net force on an object, what will happen?

A

It causes the object to accelerate in the direction of the force.

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2
Q

What equation relates force, mass and acceleration?

A

Net force (F) = Mass (m) multiplied by Acceleration (a)

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3
Q

What is the difference between mass and weight?

A

Mass is a measure of the amount of matter in an object.
Weight is a measure of the effect of gravity of mass.

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4
Q

How is weight, W, of an object calculated?

A

Weight (W) = Mass (m) multiplied by Acceleration of gravity (g)

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5
Q

What instrument can be used to determine the weight of an object?

A

A scale.

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6
Q

What is weight?

A

Weight is the measure of the force of gravity acting on a body/object.

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7
Q

What is friction?

A

Friction is a force that resists the sliding or roling of one solid object over another.

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8
Q

What is drag?

A

Drag is the oppsing force to thrust. Drag acts opposite to relative motion with respect to surrounding fluid.

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9
Q

What is tension?

A

Tension is the force transmitted through a rope, when pulled by forces acting from opposite sides.

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10
Q

What is upthrust?

A

Upthrust is a force that pushes an object upwards.

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11
Q

What is normal contact force?

A

Normal contact force is the reaction forces that acts at right angles to the surface.

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12
Q

What is meant by the term fluid?

A

Fluid is a substance that has no fixed shape.

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13
Q

How is drag related to speed?

A

As speed increases so does the collision of air molecules with the object resulting in an increase in drag. Drag is proportional to Velocty squared.

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14
Q

What is the magnitude of the drag force at the instant to object first begins to fall?

A

There will be no drag force.

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15
Q

Describe an experiment that can be conducted to investigate the motion of an object falling through a fluid.

A

You can investigate the motion of an object falling affected by a drag force using a motion sensor connected to a data-logger or a laptop. The falling object is attached to a light polystyrene ball by a thin thread passed over a pulley. The object is then dropped through a culinder of liquid such as water or glycerol, pulling the polystyrene ball vertically upwards. The motion of this ball is identical to that of the object falling through the fluid. You can generate and analyse velocity-time and acceleration-time graphs with this arrangement.

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16
Q

What is the centre of gravity?

A

The centre of gravity of an object is an imaginary point at which the object appears to act.

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17
Q

What is the centre of mass?

A

The centre of mass of an object is the point about which there is an equal distribution of mass.

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18
Q

What is the location of the centre of mass of a uniform metre ruler?

A

Around 50.0cm mark.

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19
Q

Describe an experiment that can be conductted to determine the centre of gravity of an object.

A

Make small holes along the edges of the object made from card. Insert a pin through one of the holes and into a clamp. Allow the object to swing freely untel at rest. Hang a string from the top of the pin and draw a vertical line. Find a different hole and repeat process. The centre of gravity is where the lines will intersect.

20
Q

What is meant by equilibrium?

A

When the net force and the net moment on a body is zero.

21
Q

Explain why, when an object is in equilibrium, the forces acting on it must form a closed triangle.

A

The triangle is closed because the net force is zero and so the object is in equilibrium.W

22
Q

If an object is in equilibrium, what does this mean in terms of horizontal and vertical forces acting on the object.

A

The resultant vertical and horizontal force must be zero.

23
Q

What is meant by the ‘moment of a force’?

A

‘Moment of force’ is the turning effect of a force.

24
Q

How is the moment of a force defined?

A

The moment of a force about a point is the fforce multiplied by the perpindicular distance of the line in action.

25
Q

What is the SI unit for the moment of a force?

A

The SI unit for the moment of force is Newton Metres (Nm)

26
Q

What does it mean if an object is in equilibrium?

A

When a body is in equilibrium, the net force acting on it is zero and itss net moment is zero.

27
Q

State the principle of moments.

A

When a body is balanced, the total clockwise moment about a point equals the total anti clockwise moment about the same point.
Moment = Force multiplied by Perpindicular distance from the pivot

28
Q

How can you make an object rotate without there being any translational motion?

A

To apply equal but opposite forces.

29
Q

What is a couple?

A

When a pair of equal but opposite forces are applied. Both forcess must be parallel and along different lines.
(i.e. Steering wheel)

30
Q

What is torque?

A

One force multiplied by Perpindicular seperation between forces

31
Q

What are the units of torque?

A

Newton Metres (Nm)

32
Q

How is density defined?

A

A mass of a unit volume of a material substance.

33
Q

How is density calculated?

A

Density = Mass (kg) over Volume (m^-2)

34
Q

What are the SI units of density?

A

kg/m^-3

35
Q

Describe how you would determine the density of a regular-shaped solid.

A

The volume of a regulaer-shaped solid can be calculated from measurements taken with a ruler, digital callipers, or a micrometer.

36
Q

Describe how you would determine the density of an irregular-shaped solid.

A

The volume of an irregular shape can be determined by displacement of a liquid. The difference between two water levels.

37
Q

Describe how you would determine the density of a liquid.

A

By measuring the cylinder to determine volume.

38
Q

How is pressure defined?

A

A physical force exerted on an object.

39
Q

How is pressure calculated?

A

Pressure = Force (N) over Area (m^2)

40
Q

What are the SI units of pressure?

A

Pascals (Pa)

41
Q

What is a fluid?

A

A fluid is a substance that can flow.

42
Q

Explain why gases and liquids exert pressure on surfaces?

A

Because of the constant bombardment of molecules.

43
Q

What is upthrust?

A

The upward force that a liquid or gas exerts on a body floating on it.

44
Q

Why do objects submerged in water experience an upwards force?

A

Due to differences in upper and lower pressure.

45
Q

State Archimedes’ principle.

A

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

46
Q

What condition is required for an object to sink?

A

When the upthrust is less than the weight of the object.

47
Q

What condition is required for an object to float?

A

The upthrust must equal the weight of the object.

Physics (8 decks)

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