Physics-Forces
Terms
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a force is nearly always . . .
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a push or a pull
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a force can cause change in . . .
- speed, shape or direction
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tof
forces acting on bodies act alone
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false -hardly at all
the overall effect of the forces must be considered
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if the forces acting on a body are equal and opposite, what will happen to speed and/or direction?
- speed or direction won't change
- any moving object has ____ acting against it
- friction
- if forces are balanced the object is doing one of two things. Go for it.
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- moving at a constant speed
- stationary
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resultant forces are also known as what?
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unbalanced forces
- a force is always stated as a ___ and a ____. Give the unit
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as a size (N) and a direction
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state
Newton's first law of motion
- a body stays at rest or if moving continues to move at a constant velocity unless a resultant force acts on it
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define, give units and state measuring apparatus for mass
- mass is the amount of matter contained in a body, measured in kilograms (kg) by a scale or balance
- define, give units and state measuring apparatus for weight
- weight is the force putting a body towards the center of a planet due to gravity, measured in Newtons (N) by a Newtonmeter
- give the equation for weight
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weight = mass X acceleration due to gravity
w=m X g
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Which of these changes if your on the moon (compared to earth)? How would it change?
- your mass
- your weight
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2. your weight would get lighter
NB. Your weight on the moon would be one sixth of what it is on earth.
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work is only done when a force causes movement. What's the formula for work done?
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work done = force X distanced moved in direction of force
w.d. = f X d
- what's another way of saying 1Nm?
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1 joule
NB. N X m = Nm/joule
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5kg =__ N
- 50N
- 700g = __KJ
- 0.007KJ
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work done is the same as saying . . .
- . . .energy transfered
- define and give the equation for power
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power is the rate of doing work, measured in watts
power = work done/time taken
p = w.d./t
- give all units for equation of power
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power = (kilo)Watts ((k)W)
work done = joules
time taken = seconds (not minutes!)
- 1J per second is what? (clue in the last word, the question is the answer!)
- 1W
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odd 1 out and reason why
sound, pressure, electricity, heat, light
- pressure - the rest are energy forms
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odd 1 out and reason why
oil, geothermal, solar, wind
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oil - the rest are renewable
- solar cells change ____ into ____
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light into electricity
- batteries store ______ energy
- chemical
- What's the equation for gravitational potential energy?
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PE = mass X acceleration due to gravity X difference in height
PE = m X g X h
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What's the equation for kinetic energy?
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KE = 1/2 X mass X speed squared
KE = 1/2 X m X v2
- What is all NRG measured in?
- joules
- What's the equation for efficiency?
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efficiency = useful energy out/total energy in
eff = out/in = # between 0 and 1
- All machines are less than 100% efficient. What form of energy does the waste usually take?
- sound/heat
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How is efficiency measured?
- The efficiency of something is a number from 0 to 1, sometimes given as a percentage.
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define
convection
- the flow of heat through a liquid or a gas from places of higher temperature by movement of the liquid or gas particles themselves
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define
conduction
- the flow of heat through matter from places of higher temperature. The particles don't change position, they simply vibrate. Solids are the best conductors
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define
radiation
- the flow of heat from one place to another by electromagnetic waves not needing material to pass through
- A dynamo changes ____ into ____.
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KE into electricity
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Energy cannot be created or destroyed . . .
- . . . it can only be converted from one form into another.
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A radio changes ___ into ___.
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electricity into sound
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An electric fire changes ___ into ___.
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electricity into heat/light
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An atomic bomb changes ___ into ___.
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nuclear into heat/light/kinetic/sound
- A burning candle converts ___ into ___.
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chemical into light/heat
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A jack-in-the-box converts ___ into ___.
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strain PE into KE