Riley Elwood asked "can you make a rubber band powered car out of 4 toothpicks 2 straws and 4 bottle caps". The video is virtually real time with no fast forward sections so the total build time was only about 15 minutes.

I have a separate channel focused on rubber band power - Put a rubber band on it https://bit.ly/2T3OF4j

The back toothpick simply has a very short piece of toothpick glued to it so it forms a hook to hold the band as you turn the axle.

Measurements: How long is your straw? You need holes for the axles to go through, they need to be the same position on both straws or the car will not go straight. You need holes in both straws for the cross-members to go through, they need to be the same position on both straws or the car chassis will not be straight. Other than that you can put the holes anywhere you like on the straws. Probably as near to the end of the straw as you dare without weakening the straw. If you watch the video carefully you can see I am using a ruler that is marked in centimetres and it looks like I am probably marking the holes about one centimetre from the end and then the next hole about one centimetre from that.

Making the holes might be an issue. Melting the plastic is better than trying to drill it or push a sharp spike through but it can be done. Using a hot wire or soldering iron may be a safety problem but you get a stronger hole. In the straws it is important that the holes for the cross members are a tight fit and the holes for the axles are very loose. The holes in the wheels need to be a very tight fit.

"Does adding the clay make the car move further? If so, what is the science behind it?"
The answer was already explained in the video. The car was too light so the wheels lacked grip and slipped on the floor, spinning round without moving forwards. Adding the clay to the wheels made them heavier so they had more grip, stopping them slipping, so they could drive the car forwards.
The science is about friction.

Main components
4 toothpicks
2 drinking straws
4 bottle caps
rubber bands or loom bands
hot glue
Modelling Clay for extra weight

Main Tools
Bradawl
Hot Glue Gun - If you get the relevant holes nice and tight you don't need hot glue but I like to use it.
Soldering iron - At 03:45 I explain I am using my soldering iron to melt the holes. You could just use a sharp nail or a drill but using the soldering iron means there is no chance of the plastic splitting, you need a steady hand to do it.

Snowman plays247 asked "What other types of materials can you use other than straws?". I have split the reply video over 4 episodes and placed it in it's own playlist.    • RBPC for Snowman plays247  

Some helpfiles
Rubber Band Car Hints and Tips    • Put a rubber band on it 0349 Rubber B...  
Connecting rubber bands    • Helpfile - Joining rubber bands together  
Connecting the band to the axle    • Connecting a Rubber Band to the Axle ...  
Making the CD wheels    • Helpfile - How to use Bottle Tops for...  
CD Wheels with Cardboard Hubs    • CD Wheels with Cardboard Hubs  
Putting rubber tyres on CDs    • Helpfile - how to put tyres on CDs fo...  

I recommend this alternative design - Rubber Band Powered Car 1 x size 64    • Rubber Band Powered Car 1 x size 64 -...  

Related playlist
Drinking Straw Cars    • Drinking Straw Cars  

Rubber Band Power Cars    • Rubber Band Power Cars  
Rubber Band Power playlist    • Rubber band power  
Brakes on Rubber Band Cars playlist    • Brakes on Rubber Band Cars  
Carrying Dropping Pushing Pulling Stopping playlist    • Carrying Dropping Pushing Pulling Sto...  
Rubber Band Wikipedia https://en.wikipedia.org/wiki/Rubber_...
Size 64 rubber band measure 3 1/2"x 1/4"x 1/32" or 89mm x 6mm

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