Year 4 · Angles, shapes and position
Acute and obtuse angles
Identify acute and obtuse angles and compare and order angles up to two right angles by size
Lesson overview
What you'll learn in this lesson
Identify acute and obtuse angles and compare and order angles up to two right angles by size
Key learning points
- • The right angle is your ruler
- • Turns and straight lines
- • Length does not matter
- • Putting angles in order
This lesson at a glance
- 20 minutes
- 19 parts to scroll through
- 4 quick checks
- No marked quiz yet
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 19
Watch first
Acute and obtuse angles
Learn to spot acute, right, obtuse and reflex angles anywhere.
Do it for real
The practicals below use what the film shows, with a full method you can follow at home.
In a nutshell
Identify acute and obtuse angles and compare and order angles up to two right angles by size
What you already know
Part 2 of 19
Before we start
What you already know
You can recognise a right angle in shapes around you.
Key words
Part 3 of 19
Key words
Words you'll need today
- right angle
- A quarter turn, the square corner of a page.
- acute
- Smaller than a right angle.
- obtuse
- Bigger than a right angle but less than a straight line.
Learning cycle
Part 4 of 19
Learning cycle 1 of 2
Part 1 — Naming angles
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 5 of 19
Learn
The right angle is your ruler
Hold the corner of a piece of paper against an angle. If the angle fits inside the corner it is acute. If it is wider than the corner it is obtuse. Exactly matching means a right angle.
Explore the idea
Part 6 of 19
Learn
Turns and straight lines
A quarter turn is a right angle. Two right angles make a straight line. So obtuse angles live between one and two right angles — that is exactly what 'up to two right angles' means.
Quick check
Part 7 of 19
Quick check
An angle smaller than a right angle is
Quick check
Part 8 of 19
Quick check
Two right angles together make
Reset break
Part 9 of 19
Pause
That's sitting 1 of 2 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 10 of 19
Learning cycle 2 of 2
Part 2 — Ordering angles
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 11 of 19
Learn
Length does not matter
Two angles can look different because one has longer arms, yet be the same size. Cover the arms with your fingers and look only at the opening. This is the most common trap in angle questions.
Explore the idea
Part 12 of 19
Learn
Putting angles in order
To order angles by size, sort them into acute, right and obtuse first. Then order within each group by how open they are. Tracing them onto tracing paper and laying them on top of each other settles any argument.
Quick check
Part 13 of 19
Quick check
Which is obtuse?
Quick check
Part 14 of 19
Quick check
Two angles with the same opening but different arm lengths are
Common mix-ups
Part 15 of 19
Common mix-ups
Things people often get wrong
- Judging an angle by the length of its arms.
- Calling a straight line an obtuse angle.
- Thinking acute means small and short.
Challenge round
Part 16 of 19
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 17 of 19
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
If it is wider than the corner it is ____.
Two right ____ make a straight line.
Mastery quiz
Part 18 of 19
No quiz for this one
This lesson has no marked quiz attached yet.
Lesson round-up
Part 19 of 19
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 4 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.
The cost of a school trip
A school is planning a trip to a wildlife park. The coach costs £480 however many people go. Entry costs £9.50 for each pupil and each adult goes free. The school says every pupil must pay the same amount, and the trip must not lose money.
If 60 pupils go, the coach works out at £8 each, so the total for each pupil is £17.50. If only 40 pupils go, the coach works out at £12 each, so the price rises to £21.50. The teacher explains that the coach is a fixed cost and the entry is a cost per person — which is why the price per pupil changes when the number changes.
The school decides to charge £20 and to use anything left over for a second trip later in the year.
Written for Good Learning Co.
Reading questions
- Work out the total cost of the trip if 50 pupils go.
- Show why the price per pupil falls when more pupils go, using numbers.
- At £20 each, how many pupils must go before the trip makes money? Show your working.
Working out
Working outDo the practice questions on paper, showing every step — not just the answer. Mark them yourself and circle anything you got wrong.
10–15 questions
Worked example, explained
WritingCopy one question out and write underneath, in words, why each step works.
1 question, 4–5 sentences
Problem in words
Working outWrite your own real-life problem that uses today's method, then solve it.
1 problem + solution
Saved as you type.
Part 1 of 19 · Watch & discover