Grade 6 · Science · Unit 4 of 6
Gravity & Friction
Balanced and unbalanced forces
What your child practises
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.
NWT Curriculum learning standard: Effects of balanced and unbalanced forces in daily physical activities; force of gravity; friction
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 situation shows unbalanced forces?
- a lamp hanging still from the ceiling
- a parked bike
- a book resting on a table
- a car speeding up from a red light
a car speeding up from a red light
Hint: Unbalanced forces change motion: speeding up, slowing down or turning.
Question 2
On the Moon, an astronaut dropped a hammer and a feather at the same time. What happened?
- They hit the ground at the same time
- The hammer landed first
- They floated away
- The feather landed first
They hit the ground at the same time
Hint: The Moon has no air, so there's no air resistance. Gravity makes all objects fall at the same rate.
Question 3
Why do people put oil on a bike chain?
🚲- to add weight
- to reduce friction
- to increase gravity
- to increase friction
to reduce friction
Hint: Oil makes surfaces slippery, so parts slide past each other more easily.
Question 4
A ball is thrown straight up. At the very top of its path, which force is still acting on it?
- gravity
- the force of the throw
- no forces at all
- friction from the ground
gravity
Hint: Once the ball leaves your hand, your push is gone. Gravity never stops pulling.
Question 5
Is the friction helpful or a problem? Tap an item, then tap its basket.
Sort into: 👍 helpful friction · 👎 friction is a problem
- 🚗tire treads gripping a wet road
- 📦a heavy box that's hard to slide
- 👟shoe treads gripping the gym floor
- 🚪a stiff, squeaky door hinge
- ⚙️engine parts heating up and wearing down
- ❄️sand spread on an icy sidewalk
👍 helpful friction: tire treads gripping a wet road, shoe treads gripping the gym floor, sand spread on an icy sidewalk · 👎 friction is a problem: a heavy box that's hard to slide, a stiff, squeaky door hinge, engine parts heating up and wearing down
Hint: Friction is helpful when we need grip or need to stop. It's a problem when it wears things out, wastes energy or makes things hard to move.
Question 6
In a tug-of-war, the Blue team pulls left with 600 N and the Gold team pulls right with 310 N. What is the net force on the rope?
Pulling force (N) - 290 N to the right
- 0 N (balanced)
- 910 N to the left
- 290 N to the left
290 N to the left
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.