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7th grade year > science work and machines > Flashcards

science work and machines Flashcards

1
Q

What is the formula to find work?

A

work = force X distance

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2
Q

What is the formula to find power?

A

power = work/time

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3
Q

What is the SI unit for work?

A

joules

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4
Q

What is the SI unit for power?

A

watts

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5
Q

What is the formula used to find mechanical advantage?

A

output force/input force

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6
Q

What is the formula used to find the efficiency of a machine?

A

Eff= (output work/input work) X 100

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7
Q

How can you increase the mechanical advantage of an inclined plane or wedge?

A

increasing its length (inclined plane) or by increasing its length and making it thinner (wedge)

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8
Q

How do you calculate the ideal mechanical advantage of a pulley system?

A

by counting the number of rope sections that are supporting the objects (pulling up)

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9
Q

What two machines’ mechanical advantages increase when they become longer and thinner?

A

inclined plane and wedge

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10
Q

What is the mechanical advantage of a single, fixed pulley?

A

MA = 1

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11
Q

What is the mechanical advantage of a single, movable pulley?

A

MA = 2

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12
Q

What kind of pulley is shown in the image?

What is its mechanical advantage?

A

single, movable pulley

MA = 2

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13
Q

What kind of pulley is shown?

What is its mechanical advantage?

A

single, fixed pulley

MA = 1

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14
Q

How can you determine if work is being done on an object?

A

Work is done when the object moves in the direction in which the force is being exerted.

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15
Q

A machine works by changing at least one of three factors. Name the three factors.

A
  1. A machine can change the amount of force you exert.
  2. A machine can change the distance over which you exert your force.
  3. A machine can change the direction in which you exert your force.
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16
Q

What is the difference between a real machine and an ideal machine?

A

real machines have friction and an efficiency of less than 100%

ideal machines have no friction and an efficiency of 100%

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17
Q

Would applying input force to the wheel or the axle provide for smaller input force and larger output force? Explain why.

A

Because the wheel is larger than the axle, the axle rotates and exerts a large output force. The wheel and axle increases your force, but you must exert force over a longer distance.

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18
Q

Describe the relationship between friction and the efficiency of a machine.

A
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19
Q

The thermal energy of an object depends upon what three factors?

A
  1. number of particles
  2. temperature of the object
  3. arrangement of the particles
20
Q

How are work and energy related?

A

Work is the transfer of energy.

Work requires energy.

21
Q

What is the most common energy transformation between two types of energy?

A

potential and kinetic

22
Q

How are power and energy related?

A

Power is the rate at which energy is transferred.

23
Q

What two factors affect kinetic energy?

How is KE changed when these factors are increased or decreased?

A

mass and velocity

If velocity increases, so does KE

If mass increases, so does KE.

24
Q

What is chemical energy?

A

Stored potential energy in the bonds (chemical bonds) that hold chemical compounds together

25
Q

What is thermal energy?

A

the total potential and kinetic energy of the particles in an object

26
Q

What is nuclear energy?

A

a type of potential energy stored in the nucleus of an atom

27
Q

What is electromagnetic energy?

A

energy that travels in the form of rays or waves and includes UV rays, X-rays, infrared, microwaves, visible light, radio waves, and gamma rays

28
Q

What is electrical energy?

A

the energy of moving electrical charges (electrons)

29
Q

What kind of energy do you experience when you eat a peanut butter and jelly sandwich?

A

chemical energy - in the bonds of the food

30
Q

What is energy transformation?

A

a change from one form of energy to another

31
Q

What is the law of conservation of energy?

A

When one form of energy is transformed to another, no energy is destroyed in the process

32
Q

What energy transformation is taking place when natural gas is used to heat water

A

chemical energy in gas burns and releases thermal energy

33
Q

What is convection? Give an example.

A

heat transfer by currents in a fluid - warmer, less dense fluids rise, and cooler, more dense fluids sink

  1. ocean currents
  2. air currents
  3. boiling water
34
Q

What is conduction?

Give an example.

A

Heat is transferred from one particle of matter to another without the movement of the matter

  1. icing a sprained ankle
  2. a spoon becoming hot when stirring hot chocolate
35
Q

What is radiation?

Give an example.

A

Radiation is the transfer of energy by electromagnetic waves.

feeling radiation from a fire in a fireplace

36
Q

How does a glass of soda become cold when you put ice in it?

A

The soda transfers its thermal energy to “heat” up the ice cubes which leaves the soda colder and makes the ice cubes warmer causing them to melt.

37
Q

What units would you measure energy in?

A

joules (J)

38
Q

What is the source of energy stored in fossil fuels?

A

sunlight

fusion on the sun

39
Q

List 3 conductors.

A

silver, copper, gold

40
Q

List 3 insulators.

A

wood, glass, paper, air

41
Q

In what direction does heat flow between two objects with different temperatures?

A

from warmer to colder - only one direction

42
Q

What unit is used to measure heat?

A

joules (J)

43
Q

What is the relationship between thermal energy and heat?

A

Heat is the flow of thermal energy.

44
Q

Using a flow chart, explain the energy transformations that take place when a battery is placed in an electrical circuit, and a light bulb becomes lit.

A

chemical - electrical - thermal - electromagnetic

45
Q

How does energy become stored in a fossil fuel? What kind of energy is stored?

A

Some of the sun’s electromagnetic energy is converted by photosynthesis to chemical energy called sugar and starch in the plants. Animals eat plant’s chemical energy. When the remains of dead plants and animals accumulate and are buried by sediments in swamps and marshes, the pressure and heat transform their bodies to coal, oil, and natural gas which are fossil fuels.

Fossil fuels are chemical potential energy.

46
Q

Describe how energy transformation occurs in a pendulum.

A

highest has least kinetic and most potential

lowest has most kinetic and least potential

page 456

47
Q

Explain the energy transformation involved in making hot chocolate.

Where did the energy ultimately come from? the sun

A

page 456 in text

Electricity powers the microwave oven.
Electricity is electrical energy. The microwave oven converts electrical energy into microwaves, a form of electromagnetic energy. The water absorbs the energy of the microwaves, which increases the kinetic energy of the water particles. Because the average kinetic energy of the water increases, its temperature increases. The hot water, in turn, releases thermal energy to cooler matter around it. Where did the electrical energy come from? Electrical energy can be
generated at power plants. At a power plant, large turbines rapidly spin a coil of wire within a magnet. The turbines convert kinetic energy to electrical energy. Many power plants use steam to turn the turbines. Steam is often
produced by burning coal to heat water. Burning is a chemical change in which chemical energy is changed to thermal energy and electromagnetic energy. How did coal get chemical energy? Coal is made up of the remains of
dead plants that lived miliions of years ago. When the plants died, thev were buried under layers of sediment. The pressure of these sediments, along with heat from Earth’s interior, slowly turned the plant remains into coal.
The chemical energy in coal ultimately comes from the sun. In photosynthesis, plants change the electromagnetic energy of the sun into chemical energy stored in the plant.

7th grade year (7 decks)

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