P1: Conservation And Dissipation Of Energy (Y10 - Spring 2) Flashcards
🟢 Energy Definition
Energy is the ability to work. Energy allows matter to move or cause change.
🟢 What are the 7 Energy Stores
Kinetic - In a moving object
Chemical - a fuel or battery
Gravitational - an object above ground
Elastic/Strain - a stretched or squashed object
Thermal - due to a substances temperature.
Magnetic - 2 separated magnets (attract/repel)
Nuclear - radioactive decay
🟢 How can energy be transferred (and through what pathways?)
In order to increase an energy store must be transferred between stores, this can be done through…
These 4 Pathways: (for Energy Transfer)
- Mechanically (when a force acts and something moves)
- Electricity (when a current flows)
- By Heating (because of a temperature difference)
- By Radiation (waves) (a waves such as light microwaves or sound).
🟢 What energy transfer occurs with car brake when it stops a car?
Energy from the kinetic energy store of the car is transferred via the mechanical pathway to the thermal energy store of the disc. Energy in the thermal store of the disc is transferred by the heating pathway into the thermal energy store of the surroundings and some energy of the disc is also transferred by radiation (waves) to the surrounding sound waves.
🟢 What energy transfers happen to a falling object
When an object starts to fall freely, it speeds up as it falls. The force of gravity acting on the object causes energy to be transferred from its gravitational potential energy store.
When an object hits the floor with a thud, all the energy in it’s kinetic store is tranferred by heating to the thermal energy store of the object and the floor, and by sound waves moving away from the point of impact. The amount of energy transferred by sound waves is much smaller than the amount of energy tranferred by heating.
Gravitational Potential Energy Store –> Kinetic Energy Store –>
Increase the thermal energy store
of the surroundings
/ Energy to the Surroundings
\
Increase in the thermal energy store of the
surroundings
🟢 Why is Energy Important
The concept of energy emerged in the 19th century. The idea was used to explain the work output of steam engines and then generalised to understand other heat engines. It also became a key tool for understanding chemical reactions and biological systems.
Limits to the use of fossil fuels and global warming are critical problems for this century. Physicists and engineers are working hard to identify ways to reduce our energy usage.
🟢 Example Question: Use the equation elastic potential energy = 0.5 x spring constant x (extension)^2 to calculate the maximum height the pen can reach, if the spring constant.
k = 209 N/m, the spring of the pen is compressed by e = 0.030 m, the mass of the pen m = 0.032 kg and g = 10 m/s.
Elastic potential energy = 0.5 x spring constant x (extension)^2
k = 209N/m e = 0.030m m = 0.032kg g = 10m/s
Elastic potential energy = 0.5 x 209 x 0.030^2 = 0.09405N/m
E = mhg, so h=E/mg
0.9405N/m / 0.032kg x 10m/s = 2.94m (2dp)
Answer: 2.94m (2dp)
🟢 Then, explain why the pen is unlikely to reach the height caluclated height in the example question
The pen is quite unlikely to reach the height calculated in the previous question, because there are many other factors that could come into play, like air resistance, as well as energy possibly being transferred into energy stores other than the kinetic energy store that will be needed for the pen to actually move upwards. On this point, you could also argue that if all the energy in the pen isn’t in the elastic energy store as the pen is released, then not all the energy will get to the kinetic energy store, therefore meaning the pen wouldn’t reach this maximum height calculated above.
🟢 What is The Law of Conservation of Energy
Energy can be stored and changed (transformed) from one form to another, but it can never be made or destroyed. This means that the total amount of energy in the Universe stays the same!
🟢 How does Energy change as a Pendulum Swings (assuming there is no air resistance)
As the pendulum moves to the middle, the energy from the g.p.e energy store is transferred by the force of gravity to the kinetic energy store.
The gravitational potential energy (g.p.e) store decreases as the kinetic energy store increases.
As the pendulum moves past the middle, the kinetic energy store decreases and its g.p.e store increases.
🟢 What happens to Energy when there is Air Resistance on a Pendulum
Due to air resistance some the energy is transferred to the surrounding as the pendulum swings back and forth. Therefore not all the energy is transferred between the g.p.e and kinetic energy stores on each swing meaning the pendulum does not have enough energy to return to its original starting height.
🟢 What happens to the energy in a bouncy ball when it is dropped
It initially has a store of g.p.e, but once it is dropped the g.p.e energy store decreases as the kinetic energy store increases. Energy is transferred to the surrounding through mechanical transfer by increasing the ball and surfaces thermal energy store and by sound waves.
Once the ball hits the surface it bounces upwards, increasing the g.p.e energy store and decreasing the kinetic energy store. It does not bounce back up to the original drop height. Eventually it stops bouncing.
🟢 Would a bouncy ball reached the height it was dropped from and why
The ball fall to the floor which decreases its gravitational energy store and increases its kinetic energy store.
Once it hits the surface (making a sound) it goes back upwards but not as high as where it was dropped from. As the ball bounces upwards its kinetic energy store decreases and its gravitational energy store increases.
Eventually the ball stops bouncing.
🟢 How would a bungee jumper act in a colsed system, compared to an open system.
Closed System:
The bungee jumper would be able to return to the original starting height and keep going up and down. This would be because all the energy is being transferred between the different energy stores without leaving the system.
Open System:
Some energy transferred to the cord would cause it to heat up whilst being stretched which would then transfer to the surroundings. Therefore the bungee jumper does not return to the starting height.
🟢 What does ‘Work’ mean
To actually move an object with an applied force.
