Watt's a joule?
Machinehead
Energy Never Dies
Power surge
100
When is work being done on an object?
When the force applied to the object is in the same direction that the object is moving in.
For example, when the weightlifter pushes the weights upward, he will be doing work on the weights.
100
Define work input and work output for a machine.
Work input is the work YOU do on a machine.
Work output is the work the MACHINE does on an object.
100
Why can energy never be "lost?"
The Law of Conservation of Energy states that in a closed system, energy cannot be created nor destroyed. Energy is never "lost" but it can be converted into wasted energy like thermal and/or sound energy.
100
Name 3 kinds of renewable energy.
- Solar
- Wind
- Hydropower/Ocean
- Biomass
- Geothermal
200
What are the units used to calculate and measure POWER?
Power is work divided by time.
- Power= Watts
- Work= Joules
- Time= Seconds
200
Why is a see-saw considered a machine?
A see-saw changes the direction of the input force.
200
What happens to energy when work is done on an object?
Energy is transferred to the object.
200
Name 2 drawbacks to fossil fuels.
- They are nonrenewable.
- They produce smog.
- They can release chemicals that can cause acid rain.
- They increase the risk of oil spills or other kinds of environmental problems due to the extraction of fossil fuels.
300
An elf and a giant run up a mountain. Who does more work and why?
The giant does, assuming that he weighs more than the elf.
300
What are the two simple machines that make up a pair of scissors? This is called a compound machine. One of the simple machines is a wedge and the wedge is found on the blade of the scissors.
What is the other kind of simple machine?
Scissors are made up wedges (blades) and 2 first class levers (handles).
300
When does a basketball have more GPE: right before you shoot it or when it swishes through the hoop? Explain.
When the ball swishes through the hoop because the GPE depends on the height of the object from the Earth and the weight of the object. The ball is higher when it goes through the hoop.
300
How are fossil fuels formed?
400
You lift chair that weighs 50 N to a height of 1 meter and carry it 10m across the room. How much work do you do on the chair?
You are only doing work on the chair when you lift it up.
50N x 1m = 50 J
400
Why can’t machines have 100% efficiency?
Some of the work input goes towards overcoming friction.
Work output/ work input x 100= mechanical efficiency
The work output is always smaller than the work input. This also means that some energy is converted into thermal energy.
Work output/ work input x 100= mechanical efficiency
The work output is always smaller than the work input. This also means that some energy is converted into thermal energy.
400
Which has more KINETIC ENERGY: a porcupine, kangaroo, or mouse running at 15 m/s? Please explain.
Kinetic energy depends on the mass of the object and the speed. Since all of these animals are traveling at the same speed, the one with the largest mass would have the most KE: the kangaroo.
400
What kinds of energy conversions occur when burning a piece of firewood?
Chemical energy is converted into:
thermal energy- We feel the heat.
sound energy- We hear the firewood crackling.
kinetic energy-Some of the wood moves when burned.
500
Why is the unit for energy and work the same?
Because work and energy are related. When work is done, energy is transferred. Energy allows work to be done.
500
What does it mean if one machine has a greater mechanical advantage than another machine?
It means that one machine increases the output force with the same amount of input force as a machine with less mechanical advantage.
Mechanical advantage= output force/ input force
Mechanical advantage= output force/ input force
500
Which has more thermal energy: a small cup of hot water or a swimming pool of lukewarm water? Please explain.
Thermal energy is the total kinetic energy of the particles in an object. Since kinetic energy depends on mass and the speed...thermal energy depends on the number of particles (mass) and the speed of the particles. The swimming pool as much more mass than a small cup of water. The swimming pool has more thermal energy.
500
Why does burning a fossil fuel release more energy than burning firewood?
Both fossil fuels and firewood store energy from the sun. However, fossil fuel is a more concentrated source so when it is burned, much more energy is released.