6th grade · Science · Unit 5 of 17
Gravity & Friction
Balanced and unbalanced forces
What your child practices
Working out net force, telling balanced from unbalanced forces, mass versus weight on the Moon and other planets, and when friction helps or causes problems.
Texas Essential Knowledge and Skills (TEKS) teks student expectation: 6.7(A); 6.7(B) · gravity, friction and applied forces, net force, and balanced and unbalanced forces
How we explain it
Children can open this short lesson before they practice.
- Gravity is a force of attraction between objects that have mass.
- Mass is the amount of matter. Weight is the pull of gravity on that mass.
- Friction slows sliding objects. Rough surfaces like carpet give more friction.
- Air resistance slows light, spread-out objects like feathers. Unbalanced forces change motion.
Example: A puck slides on ice, wood and carpet. Where does it slow down fastest? Rougher surfaces make more friction. Carpet is the roughest. Answer: on carpet
Gravity & Friction in Texas
In the Texas Essential Knowledge and Skills (TEKS), this is unit 5 of 17 in 6th grade Science, after Chemical Reactions and before Newton's Laws.
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
On Earth, why does a feather fall more slowly than a rock?
- Gravity pulls light things upward
- Gravity doesn't pull on feathers
- Air resistance slows the feather much more
- The feather has more mass
Air resistance slows the feather much more
Hint: The feather is light and spread out, so the air pushes back on it a lot compared to its weight.
Question 2
In a tug-of-war, the Blue team pulls left with 530 N and the Gold team pulls right with 600 N. What is the net force on the rope?
Pulling force (N) - 1130 N to the right
- 70 N to the left
- 0 N (balanced)
- 70 N to the right
70 N to the right
Hint: When forces point in opposite directions, subtract the smaller from the larger. The net force points the way of the bigger force. Equal forces are balanced: the net force is 0 N.
Question 3
Why do many drivers put winter tires on their cars?
❄️- They remove all friction
- Their treads give more friction on snow and ice
- They reduce gravity
- They make the car lighter
Their treads give more friction on snow and ice
Hint: More grip (friction) helps a car start, turn and stop safely on slippery roads.
Question 4
The Moon's gravity is about 1/6 as strong as Earth's. A rover weighs 180 N on Earth. About how much does it weigh on the Moon?
🌙answer boxN
30 N
Hint: Weight is the pull of gravity. With 1/6 of the gravity, the rover weighs 1/6 as much, so divide its Earth weight by 6.
Question 5
Which force keeps the Moon in orbit around Earth?
🌙- magnetism
- air resistance
- friction
- gravity
gravity
Hint: Earth's pull keeps tugging the Moon toward it, bending its path into an orbit.
Question 6
What is friction?
- a force that only acts in space
- a force that resists motion when surfaces rub together
- the speed of a moving object
- a force that pulls objects toward Earth
a force that resists motion when surfaces rub together
Hint: Rub your hands together. The force you feel resisting the motion is friction.