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# Stjernetårnet - a Family Free Fall Tower

Take a look a the sequence of screen shots from a ride in a similar tower (Stjernetårnet in Tivoli gardens). Where are you moving faster and where are you moving slower. Where do you feel heavier than normal and where do you feel light. If you ask nicely, you may be able to bring a short plastic spiral (slinky) when your ride. Attach it to your middle finger using a rubber hand. Keep the hand stretched and don't move it, while you observe the motion. How long is the slinky ...

• ... when you move up in the beginning of the ride?
• ... when you turn in the highest point?
• ... when you are on your way down?
• ... when you turn in the lowest point?
• ... when you are on your way up again?

The slinky illustrates the forces acting on (and in) your body. If you look carefully at the sequence, you may see that the person to the right in the image holds a short slinky changing the length while the ride is moving. The sequence below shows a series of closup screen shots of the slinky.

Instead of a slinky, you may be able measure the forces using a smartphone accelerometer. The graph to the right shows the "G force" on the body during a ride. The graph below shows an image of the velocity during two bounces (based on the accelerometer data).

In which of the points marked ..

• ... is the ride in the highest point?
• ... is the ride in the lowest point?
• ... does the ride move fastest?
• ... does the ride move slowest?
• ... would a rider feel heaviest?
• ... would a rider feel the lightest?

Check your answer on the image showing height, velocity and acceleration during two bounces.

Read more about investigations in the Stjernetårnet and similar rides in the paper Up and down, light and heavy, fast and slow - but where? in Physics Education 54 2 025017 (2019)

Also watch movie of the ride.