Topic 8 - forces doing work

0.0(0)
learnLearn
examPractice Test
spaced repetitionSpaced Repetition
heart puzzleMatch
flashcardsFlashcards
Card Sorting

1/12

encourage image

There's no tags or description

Looks like no tags are added yet.

Study Analytics
Name
Mastery
Learn
Test
Matching
Spaced

No study sessions yet.

13 Terms

1
New cards

state the law of energy conservation

energy cannot be created or destroyed (it can only be transferred into different forms)

2
New cards

describe the energy changes involved when a ball is thrown upwards and then returns to its starting position. (ignore air resistance)

  • upwards: KE is converted to GPE

  • peak: maximum GPE, zero KE

  • downwards: GPE is converted to KE

3
New cards

energy in a system

  • when a system changes, energy is transferred from one form to another

    • electrical energy changes into kinetic energy in a motor

4
New cards

what is a closed system

  • a closed system is a system which experiences no external forces

    • eg. a circuit, or a skydiver

    • in a closed system, the total energy remains the same at all times

5
New cards

equation for change in gravitational potential energy

change in gravitational potential energy (joule, J) = mass (kilogram, kg) x gravitational field strength (newton per kilogram, N/kg) x change in vertical height (metre)

<p>change in gravitational potential energy (joule, J) = mass (kilogram, kg) x gravitational field strength (newton per kilogram, N/kg) x change in vertical height (metre)</p>
6
New cards

formula for kinetic energy

kinetic energy (joule, J) = ½ x mass (kilogram, kg) x (speed)²((metre/second²),m/s)²)

<p>kinetic energy (joule, J) = ½ x mass (kilogram, kg) x (speed)²((metre/second²),m/s)²)</p>
7
New cards

changes

  • work done

    • this is when an external force transfers energy to a system

    • eg. a human doing work to push a ball up a hill

  • electric

    • chemical potential energy (stored in batteries) forms electirc

  • heating

    • electric transfers to thermal energy, as work is done against the heating coils causing it to heat up

8
New cards

equation for work done

work done (joule, J) = force (newton, N) x distance moved in the direction of the force (metre, m)

<p>work done (joule, J) = force (newton, N) x distance moved in the direction of the force (metre, m)</p>
9
New cards

waste

  • energy is rarely 100% transferred into the desired form

    • some energy is dissipated so it is stored in less useful ways

  • mechanical processes are wasteful when they get hot (usually due to friction)

    • energy is dissipated as heat, causing a rise in temperature

    • so the energy is lost to the surroundings

10
New cards

what is power and equation for it

  • the rate at which energy is transferred

  • power (watt, W) = energy transferred or work done (joule, J)/time taken (second, s), where 1 watt is equal to 1 joule per second

<ul><li><p>the rate at which energy is transferred </p></li><li><p>power (watt, W) = energy transferred or work done (joule, J)/time taken (second, s), where 1 watt is equal to 1 joule per second</p></li></ul><p></p>
11
New cards

what is efficiency

  • measure of how much energy is not lost as waste

12
New cards

efficiency equation

efficiency = useful output energy/total input energy

13
New cards

one watt in joule per second

1 watt = 1 J/s