FYI:
The objects whose speed are to be measured should be any opaque object(small or big) that has no gap in between (a gap where light could pass through).

It should be able to display the speed of a really slow thing such as a person walking to a really fast thing such as a car zooming past.

The distance between the two lasers will be really small(like half a centimeter) so that it can be easy to move around.

The laser I'm planning to use is a conventional laser pointer that's wired to a regulated power supply so that it would automatically stay on as soon as the device is turned on.

I'm still deciding whether to use a photodiode or transistor.

P.S.
Nice point BobK - I'll ask for help after trying to solve any problems I encounter myself. But I'm open to suggestion.