1. First, invest in a spare inner tube. If you get a puncture on the road it's far easier to change the tube and repair the punctured one later at home. To repair the tube you'll need a pump, tyre levers and a puncture repair kit with patches, sandpaper, a marker and glue.
Mass is a measure of the number of atoms in an object combined with the density of those atoms. Usually people measure mass in kilograms. You can tell how much mass something has by measuring how hard it is to get that thing to change directions or slow down. If you're driving a big truck, for instance, you're going to need a lot stronger brakes to stop the truck than if you were riding a bicycle.
An atomic mass (symbol: m a) is the mass of a single atom of a chemical element. It includes the masses of the 3 subatomic particles that make up an atom: protons, neutrons and electrons. Atomic mass can be expressed in grams. However, because individual atoms have very small masses, this is not very helpful. Instead, atomic mass is expressed in unified atomic mass units (unit symbol: u). 1 atomic mass unit is defined as 1/12 of the mass of a single carbon-12 atom.