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6th grade · Science · Unit 6 of 10

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.

New York State Learning Standards 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 New York

In the New York State Learning Standards, this is unit 6 of 10 in 6th grade Science, after Thermal Energy & Insulation and before Weather Systems.

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: New York State Education Department (NYSED)

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

    The force on a cart doubles and the distance stays the same. What happens to the work?

    • It halves.
    • It becomes zero.
    • It stays the same.
    • It doubles.

  2. Question 2

    A force of 10 N does 80 J of work. How far, in m, did the object move?

    answer boxm

  3. Question 3

    An LED bulb is more efficient than an incandescent bulb because it…

    • produces more heat
    • turns more of the electrical energy into light
    • is made of glass
    • uses no electricity

  4. Question 4

    A motor takes in 400 J of energy and gives 320 J of useful energy. What is its efficiency, in %?

    answer box%

  5. Question 5

    A force of 40 N moves a crate 9 m in the direction of the force. How much work is done, in J?

    answer boxJ

  6. Question 6

    Efficiency compares…

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

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