A fun, simple, and cheap project for kids, and you can make more than one and race them.
Step 1: Materials
Double sided tape strip
Disc battery (any kind)
Vibrating motor (any kind)
Some sort of strong cutting tool
Step 2: Cutting the Toothbrush
The first step is taking a strong cutting tool and cutting off the head of the toothbrush. The bristles may have to be cut with scissors to have them the same length.
Step 3: Cutting the Tape Strip
Next cut the tape strip with scissors to fit the top of the toothbrush head and place it on top.
Step 4: Attaching the Motor
Place the motor on one end of the tape strip with the wires facing the empty side.
Step 5: Place the Battery
The battery can be placed either on one of its sides flat, or on standing up. It might work better with the wire standing up, but being flat is better for balance.
Step 6: Connecting the Motor to the Battery
The final step is placing the wires on either side of the battery. The charge of the sides does not matter, and the best and safest way to keep the wires attached it electric tape. To make sure the battery doesn't run out, leave one wire unattached when not in use.