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6th grade · Science · Unit 6 of 6

Work, Energy & Efficiency

Force, distance and wasted energy

What your child practices

Using the scientific terms force, displacement, work, energy and efficiency, calculating work as force times displacement, finding efficiency, and how friction and design affect the energy lost from machines.

Maine Learning Results learning standard: MS-PS3-5 · when an object's kinetic energy changes, energy is transferred to or from it, as in work

How we explain it

Children can open this short lesson before they practice.

  1. In science, work means a force moves something a distance: work = force × distance.
  2. Work and energy are measured in joules (J).
  3. No machine is perfect: some energy is wasted, often as heat.
  4. Efficiency = useful energy out ÷ energy in × 100%.

Example: A motor takes in 500 J and gives 350 J of useful energy. What is its efficiency? Efficiency = useful ÷ total × 100%. 350 ÷ 500 = 0.7. 0.7 × 100% = 70%. Answer: 70%

Work, Energy & Efficiency in Maine

In the Maine Learning Results, this is unit 6 of 6 in 6th grade Science, after Engineering Design.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Maine Department of Education

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Efficiency compares…

    • mass with volume
    • force with distance
    • speed with time
    • useful energy output with total energy input

  2. Question 2

    Which formula gives work?

    • work = displacement ÷ force
    • work = force ÷ displacement
    • work = force + displacement
    • work = force × displacement

  3. Question 3

    A motor takes in 200 J of energy and gives 80 J of useful energy. What is its efficiency, in %?

    answer box%

  4. Question 4

    A force of 25 N moves a crate 2 m in the direction of the force. How much work is done, in J?

    answer boxJ

  5. Question 5

    When we say energy dissipates from a machine, we mean it…

    • is stored forever
    • turns into mass
    • is destroyed
    • spreads out as less useful energy, such as heat and sound

  6. Question 6

    A force of 10 N does 20 J of work. How far, in m, did the object move?

    answer boxm

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