Subscribe

8th grade · Science · Unit 10 of 16

Newton's Laws

Three laws of motion

What your child practices

Inertia (1st law), force = mass × acceleration (2nd law) and action–reaction pairs (3rd law), with everyday examples and a few simple calculations.

Alabama Course of Study content standard: 8.11 · Newton's three laws of motion and net force

How we explain it

Children can open this short lesson before they practice.

  1. First law (inertia): an object keeps doing what it is doing unless an unbalanced force acts.
  2. Second law: force = mass × acceleration. Force is measured in newtons (N).
  3. Third law: every action has an equal and opposite reaction.

Example: A 3 kg ball accelerates at 5 m/s². What force acts on it? F = m × a. 3 × 5 = 15. Answer: 15 N

Newton's Laws in Alabama

In the Alabama Course of Study, this is unit 10 of 16 in 8th grade Science, after Motion, Forces & Newton’s Laws and before Fields & Forces at a Distance.

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: Alabama State Department of Education (ALSDE)

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

    A swimmer pushes off the pool wall. Which force moves the swimmer forward?

    🏊
    • the water's friction
    • gravity
    • the swimmer pushing on the wall
    • the wall pushing back on the swimmer

  2. Question 2

    Newton's first law is also called the law of…

    • inertia
    • friction
    • reflection
    • gravity

  3. Question 3

    A 10 kg wagon speeds up at 6 m/s². What net force is acting on it?

    F = m × a

    answer boxN

  4. Question 4

    What is inertia?

    • the rubbing of two surfaces
    • an object's resistance to a change in its motion
    • how bright an object is
    • the force that pulls objects toward Earth

  5. Question 5

    A soccer ball sits still on the grass. What will make it start moving?

    ⚽
    • balanced forces
    • its own inertia
    • waiting long enough
    • an unbalanced force, like a kick

  6. Question 6

    A bus stops suddenly and the riders lurch forward. Why?

    🚌
    • Their bodies keep moving forward because of inertia
    • The bus pushes them forward
    • The bus floor pulls them forward
    • Gravity pulls them forward

More 8th grade