search

phetsims / energy-skate-park

"Energy Skate Park" is an educational simulation in HTML5, by PhET Interactive Simulations.
MIT License
2 stars 11 forks source link

[Measure Screen] Round height and speed readouts to the hundredths place #291

Closed arouinfar closed 4 years ago

arouinfar commented 4 years ago

Tangential to https://github.com/phetsims/QA/issues/544

A user wrote into phethelp:

Hello,

I am currently a physics lecturer at Indonesia. I try this simulation but I don’t quite understand the value for the energy measured in the simulation.

As you can see below that the potential energy is 2385.3 J and the height is 4.1 m, but if I use mgh it will give 2587.2 J (mass is 60 and g is 9.8). Same thing happen for kinetic energy. image

Can you explain? I might miss something here.

The discrepancy is due to the rounding of the height and speed readouts. Calculating the height from the PE results in 4.0566 m, which rounds to 4.1 m. Similarly, calculating the speed from the KE results in 7.2613 m/s which rounds to 7.3 m/s.

It is not unreasonable for users to calculate the PE/KE from the height/speed readouts. With only one decimal place, the calculated energies are often off by ~25 J. Adding a 2nd decimal place reduces the discrepancy to ~1-2 J which I think is more acceptable.

@jessegreenberg please update the height and speed readouts to round to the hundredths place.

jessegreenberg commented 4 years ago

Rounded to the hundredths place in the above commit. Will also cherry-pick into release branch.

jessegreenberg commented 4 years ago

cherry-picked into 1.0 (protoytpe branch) and 1.1 (rc branch). @arouinfar can you please review?

arouinfar commented 4 years ago

Looks good in master, thanks @jessegreenberg!