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5th grade · Science · Unit 4 of 15

Forces, Friction and Machines

Pushes, pulls and rubbing surfaces

What your child practices

Forces as pushes, pulls and twists, how friction affects motion, and how friction makes simple machines less efficient.

Texas Essential Knowledge and Skills (TEKS) teks student expectation: 5.7(A); 5.7(B) · how forces, including friction, change motion, and testing their effects

How we explain it

Children can open this short lesson before they practice.

  1. Friction is a force from surfaces rubbing. It slows things and makes heat.
  2. Smooth or oiled surfaces reduce friction, like wax on sled runners.
  3. Rough surfaces add friction, like sand on ice.
  4. Simple machines make work easier by changing a force's size or direction. An axe blade is a wedge.

Example: Why do people put oil on a bike chain? Oil makes the parts slide past each other smoothly. That means less rubbing. Answer: to reduce friction

Forces, Friction and Machines in Texas

In the Texas Essential Knowledge and Skills (TEKS), this is unit 4 of 15 in 5th grade Science, after Solid, Liquid, Gas and before Forms of Energy.

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: Texas Education Agency (TEA)

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

    Rubbing your hands together makes them warm. Why?

    • the force disappears
    • friction produces heat
    • your hands get lighter

  2. Question 2

    Why do bike tires have treads?

    • to make the bike lighter
    • to grip the road
    • to make noise

  3. Question 3

    Which is a wedge?

    • an axe blade
    • a flagpole
    • a wheelbarrow wheel

  4. Question 4

    A hockey puck slides far on ice because…

    • there is a lot of friction
    • gravity is off
    • there is little friction

  5. Question 5

    Which surface has the most friction?

    • polished glass
    • ice
    • sandpaper

  6. Question 6

    Which is a benefit of friction?

    • a drawer sticking
    • brakes stopping a bike
    • a machine heating up and wearing out

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