Modelling the DART impact with trolleys
The question
How does throwing material backwards in a collision increase the push given to the target?
In 2022 NASA's DART spacecraft hit the asteroid moonlet Dimorphos and shortened its orbit by about 32 minutes. The rock blasted off the surface gave an extra push, so the asteroid received more momentum than the spacecraft carried.
Equipment
- Two dynamics trolleys on a level runway, or an air track
- Light gates and a data logger, or a phone video with a scale
- Plasticine, Velcro and a set of masses
- A balance
Method
- Measure the masses. Roll the moving trolley (the spacecraft) into the stationary one (the asteroid) with plasticine so they stick together. Measure speeds before and after.
- Check that momentum (mass × velocity) is conserved.
- Model ejecta: fix a spring-loaded plunger to the target, so that on impact it releases a small mass that flies backwards, towards where the spacecraft came from. Measure the target's speed again.
- Compare the momentum gained by the target with and without the ejecta.
- What to measure
- Masses and velocities before and after each collision; momentum before and after; the ratio of momentum gained by the target to momentum delivered (scientists call this β).
- How to present it
- A table and bar chart of momentum, your value of β, and an explanation of why ejecta made DART more effective.
- Take it further
- Find out what the Hera mission will measure at Dimorphos and why the mass of the asteroid matters for β.
Safety
Keep runways on the floor or bench with end stops so trolleys cannot fall; keep fingers clear of the plunger.