From a computer:
1) Use iTunes File Sharing to transfer a file to your device.
2) In Video Physics on your device, tap the + button to start a new experiment, then choose, “iTunes File Sharing.”

For more on iTunes File Sharing, see:

To transfer the video from one device to another, open an Experiment and tap the Share button. You can send files via Mail, Messages, AirDrop, or third-party apps, such as Dropbox or Google Drive.

Some third-party mail clients on iOS do not properly allow you to open attachments into Video Physics. If you have issues, try using the built-in Mail client.

See also:
Can I use Vernier Video Physics with my Dropbox account?