Electrons slow down as they travel through a wire because they hit the fixed atoms of the conducting metal in an occurrence called resistance. The longer the wire, the fewer electrons are able to reach the end of it.
When electricity flows through a wire, its electrons must move past the individual atoms of the wire material. These impacts slow down the electrons and can eventually stop their flow. There are a few factors that affect how much resistance electricity encounters, including the width of the wire, the wire material and the length of the wire.
A longer wire requires more width and should be made of a material that is highly conductive to cut down on resistance. The electricity naturally flows through wider wires at a much higher rate compared to a narrow wire. This means that resistance takes a greater distance to stop the flow rate and that resistance overall is lessened.
The wire material is also an important factor to consider, as it can affect the wire length that can be used on a project. Highly conductive materials like silver and copper offer the least amount of resistance to the flow of electrons compared to a highly resistant material like rubber. High quality copper cables can carry electrons quite far without much loss in the flow rate, but they are more expensive materials.