Spread your hands as far apart as you can along the broom.
Pick up the broom using only one finger of each hand… it’ll be heavy on the broom end.
Slowly slide you fingers together at the same speed.
You will find that the finger close to the broom head doesn’t move much compared to other finger.
Once you get your fingers together you have found the broom’s centre of gravity.
Can you balance the whole broom using one finger on that point?
Try other odd shaped objects, e.g. baseball bats, golf clubs and hockey sticks… be careful!
Try repeating the experiment, only placing your hands in a different spot.
Do you find the centre of gravity each time no matter what?
Get the Unit of Work on Forces here!
- Push, pull
- Friction & spin!
From inertia to centripetal force, this unit covers many concepts about Newton’s Laws!
Includes cross-curricular teaching ideas, student quizzes, a sample marking rubric, scope & sequences & more
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Why Does This Happen
Every object has a centre of gravity, only it is in a different place for different shaped objects.
The centre of gravity is where the mass of the object is equally balanced. By sliding your fingers along the bottom of the broom, you found the natural centre of balance.
Applications
Centre of balance is critically important to everything that moves (or stands still!). From spinning ice skaters to spaghetti towers, understanding where your centre of balance can be found makes a huge difference.
- If you lean too far forward you will start to fall… why? Because most of your mass is away from your centre of gravity, causing you to fall to the ground. Living things very quickly learn about their centre of balance when they’re learning to move.
- Engineers and builders use the centre of balance when designing machines, buildings, bridges and more.
- The centre of balance in a rock formation determines whether a landslide will occur.
- If you’ve ever overstacked your dishes in the sink, you’ve watched the impact of centres of balance as your dishes fall!
Variables to test
- Try different brooms, does this demonstration work every time?
- What happens if you pull off the end of the broom?
- Try this with other things such as a kayak paddle, a mop, a rake and so on.
- Teaching about Newton’s laws? Check out the Forces, Friction & Movement workshop!
Get in touch with FizzicsEd to find out how we can work with your class.
Forces, Friction & Movement
Years K to 6
Maximum 30 students
School workshop
60 or 90 minutes
Online Class Available
STEM Full Day Accelerator - Primary
Designed from real classroom experiences, this modular day helps you create consistently effective science learning that directly address the new curriculum with easily accessible and cost-effective materials.
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