6th grade · Science · Unit 6 of 17
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.
Texas Essential Knowledge and Skills (TEKS) teks student expectation: 6.7(C) · equal and opposite force pairs (Newton's third law)
How we explain it
Children can open this short lesson before they practice.
- First law (inertia): an object keeps doing what it's doing unless a force acts on it.
- Second law: net force = mass × acceleration. Force is measured in newtons (N).
- Third law: every action has an equal and opposite reaction.
- Friction is a force that slows things, so a puck slides farther on smooth ice.
Example: A 30 kg cart speeds up at 2 m/s². What net force acts on it? Force = mass × acceleration. 30 × 2 = 60. Answer: 60 N
Newton's Laws in Texas
In the Texas Essential Knowledge and Skills (TEKS), this is unit 6 of 17 in 6th grade Science, after Gravity & Friction and before Kinetic & Potential 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.
Question 1
Which of Newton's laws does each example show? Tap an item, then tap its basket.
Sort into: 1️⃣ 1st law: inertia · 2️⃣ 2nd law: F = m × a · 3️⃣ 3rd law: action and reaction
- 🚀A rocket pushes gas down and the gas pushes it up
- 🏊A swimmer pushes water back to move forward
- ⚾A harder throw makes a ball go faster
- ⚽A ball sits still until someone kicks it
- 🚚A loaded truck needs more force to speed up than a bike
- 🏒A puck keeps gliding on smooth ice
1️⃣ 1st law: inertia: A ball sits still until someone kicks it, A puck keeps gliding on smooth ice · 2️⃣ 2nd law: F = m × a: A harder throw makes a ball go faster, A loaded truck needs more force to speed up than a bike · 3️⃣ 3rd law: action and reaction: A rocket pushes gas down and the gas pushes it up, A swimmer pushes water back to move forward
Hint: 1st law: things keep doing what they're doing (inertia). 2nd law: more force or less mass means more acceleration. 3rd law: every push has an equal push back.
Question 2
How does a rocket lift off?
🚀- Gravity pulls it upward
- Its wings lift it like a plane
- It pushes hot gases down, and the gases push the rocket up
- It pushes against the air above it
It pushes hot gases down, and the gases push the rocket up
Hint: That's Newton's third law: action (gas pushed down) and reaction (rocket pushed up). It even works in space, where there's no air.
Question 3
What is inertia?
- the rubbing of two surfaces
- how bright an object is
- an object's resistance to a change in its motion
- the force that pulls objects toward Earth
an object's resistance to a change in its motion
Hint: A still object stays still and a moving object keeps moving, unless a force changes it.
Question 4
A 60 kg wagon speeds up at 3 m/s². What net force is acting on it?
F = m × a
answer boxN
180 N
Hint: Newton's second law: force = mass × acceleration. Multiply the mass in kilograms by the acceleration.
Question 5
An astronaut floating outside the space station throws a tool forward. What happens to the astronaut?
👩🚀- Nothing happens to the astronaut
- The astronaut falls to Earth
- The astronaut drifts backward
- The astronaut drifts forward
The astronaut drifts backward
Hint: The astronaut pushes the tool forward, so the tool pushes the astronaut backward.
Question 6
Action and reaction forces are equal and opposite. Why don't they cancel out?
- They happen at different times
- They act on different objects
- They do cancel, so nothing ever moves
- One is always a bit bigger
They act on different objects
Hint: When you push a wall, your push acts on the wall and the wall's push acts on you. Forces only cancel when they act on the same object.