Episode 12: Ping Pong Pick Up
Join us this week for a challenge that’s perfect for whenever you need a “pick me up”. Lift your spirits at the same time as your ping pong balls when you challenge your family to a game of… Ping Pong Pick Up.
Before you start
These experiments have not been specifically safety tested for home use but we believe them to be safe if the instructions are followed. Adult supervision or direction is recommended as appropriate. All experiments are carried out at your own risk.
What you’ll need
- A large, empty plastic bottle – we’ve used a two litre fizzy drink one
- Sticky tape
- A marker pen
- A bowl
- A few ping pong balls / anything small and round
- A mug (or anything circular to draw around that’s wider than a ping pong ball but not as wide as the bottle)
What to do
Make sure you supervise this experiment very carefully. We’re using sharp scissors as a piercing tool – combined with the risk of ping pong balls flying everywhere. You might need to do some steps either with (or for) your family depending on their ages and how sensible they are.
Before you can start to play, you need to make your “picker-upper”.
- Turn your bottle upside down and put it in the mug. Using the mug as a template, draw a circle on your bottle in marker pen and take the bottle out again.
- Cut along the line you’ve drawn. To get started you have to stab a hole in the bottle first using the pointy end of your scissors. An adult should definitely do this part.
- We’re only using the bottom of the bottle – it should look like a tall container with a small curved lip. If you’ve made any sharp or jagged edges with your scissors, cover them up with sticky tape so that your “picker-upper” is safe to hold and use. Now you’re ready to play Ping Pong Pick Up.
- Challenge your family to pick up the ball without touching it or turning the bottle, and then drop it into the bowl. Once they’ve tried – show them how it’s done.
- With the ball on your table, grip the picker-upper firmly. Put it over the ball and start moving the bottle in small, fast circles.
- Once you’ve got the ball spinning, lift it up (anyone else in the room should watch out for flying ping pong balls in case it goes wrong!) and drop it into the bowl.
- And then it’s a case of practice makes perfect! The challenge is to get the ball as quickly as possible from table to bowl.
What to talk about
- Does the picker-upper have to be a special shape for it to work?
- What happens if your hand gets tired and you slow down?
What’s going on?
It’s the shape of the ping-pong-picker-upper that’s at the heart of this challenge. You can’t just use anything!
Think about a ball moving around inside a straight-sided container like a plastic glass. As it spins, the ball wants to fly out but the glass won’t let it. As it presses on the inside wall of the container, the wall pushes back and it is this force that makes the ball goes around in a circle. But a straight-sided container can’t pick up the ball, it only pushes inwards. To lift the ball, we need an upward push to overcome gravity.
Our picker-upper has sloped walls and that’s why it works. The push of the wall on the ball is diagonally upwards and we can think of this force as having two parts: an inwards part that makes the ball go around in a circle, and an upwards part that balances the downward pull of gravity.
The upwards and inward parts are called the vertical and horizontal components. If you keep the ball spinning quickly you can balance gravity using the vertical force component.
The game should work with any round object inside a container with a mouth narrower than its body. You could:
- experiment to see how high you can lift the ping pong ball
- challenge yourself by moving your bowl further away or using a smaller container for drop off
- challenge the adults in the house to a game with wine glasses and Maltesers
Did you know
As part of their training, astronauts are spun just like a ping pong ball in a picker-upper. The sideways push of the wall recreates the large forces they experience when launching into space.
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