Balanced and unbalanced forces
Forces come in pairs and are measured in newtons. What matters is not whether forces act, but whether they cancel.
Part of your national curriculum
- Physics: motion and forces: Understand forces as pushes or pulls arising from the interaction between two objects, and balanced and unbalanced forces
Lesson overview
What you'll learn in this lesson
Describe balanced and unbalanced forces
Key learning points
- • Resultant force
- • Friction and drag
This lesson at a glance
- 25 minutes
- 10 parts to scroll through
- 3 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 10
Watch first
Balanced and unbalanced forces
An English teaching video on this topic from MrE Science. Watch it, then scroll down for the lesson.
In a nutshell
Describe balanced and unbalanced forces
Explore the idea
Part 2 of 10
Learn
Resultant force
Balanced forces give zero resultant: the object stays still or keeps a constant speed. Unbalanced forces change speed or direction.
Explore the idea
Part 3 of 10
Learn
Friction and drag
Friction opposes motion between surfaces; drag opposes motion through fluids. Terminal velocity is reached when drag balances weight.
Quick check
Part 4 of 10
Quick check
Balanced forces mean the object…
Quick check
Part 5 of 10
Quick check
Forces are measured in…
Quick check
Part 6 of 10
Quick check
Terminal velocity happens when…
Challenge round
Part 7 of 10
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 8 of 10
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
____ forces give zero resultant: the object stays still or keeps a constant speed.
____ forces change speed or direction.
____ opposes motion between surfaces; drag opposes motion through fluids.
Mastery quiz
Part 9 of 10
Marked quiz
End of lesson quiz: Balanced and unbalanced forces
3 questions, marked with the reasoning shown. No timer.
1. Balanced forces mean the object…
2. Forces are measured in…
3. Terminal velocity happens when…
Lesson round-up
Part 10 of 10
Lesson round-up
Ready when you are
Quiz score
Not sat
Games
Not played
Points this lesson
0
Best run
0 in a row
Luna: 0 out of 3 on the practice checks. Only if you feel up to it — one more?
Ask LunaDo the work
Your written work for this lesson
This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.
Why the school greenhouse failed
A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.
The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.
The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.
Written for Good Learning Co.
Reading questions
- Name the variable the club changed the second time, and one variable they kept the same.
- Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
- Write a conclusion for the club's report, saying how far the evidence supports it.
Method and results
WritingWrite the aim, what you changed, what you measured and what you kept the same, then record your results in a table.
1 page + results table
Conclusion
WritingExplain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.
6–8 sentences
Labelled diagram
DiagramDraw the apparatus or the process in pencil, label it fully, and photograph it.
1 labelled diagram
Reading and notes
ReadingRead the lesson text again and write the key ideas in your own words.
Half a page of notes
Saved as you type.
Part 1 of 10 · Watch & discover
How this is going
- Not looked at yet
Understand forces as pushes or pulls arising from the interaction between two objects, and balanced and unbalanced forces