Mass is a measure of the amount of matter contained in an object. The denser an object is, the greater its mass will be. Mass is not to be confused with volume, as volume is a measure of how much space an object occupies. When you want to quantify the amount of mass an object has, you must measure it using a triple beam balance. The object is placed on one end of the triple beam balance and the sliding weights are moved forward until both sides are in equilibrium. A triple beam balance is used to measure mass because it allows you to compare the unknown mass of an object against the known masses of the beams.
Kinetic energy is the energy an object produces because of its motion. The kinetic energy of an object can be used to perform work on another object. For example, when you roll a bowling ball down the lane, your bowling ball possesses kinetic energy, which can be used to knock down the pins at the end of the lane. The velocity at which an object is sent moving and the mass of the object both play a hand in the level of kinetic energy that object produces.
Mass and kinetic energy have a positive relationship, which means that as mass increases, kinetic energy increases, if all other factors are held constant. For example, an inflatable beach ball rolled down a bowling lane at a velocity of 5 meters per second would not have as much kinetic energy as a bowling ball rolled down a bowling lane at the same velocity because the bowling ball has a greater mass, thus producing a greater amount of kinetic energy.
Decreases in mass cause decreases in kinetic energy due to the aforementioned positive relationship between the two. It is important to keep in mind that the relationship only holds if all other things remain constant. Therefore, in a scenario where mass is decreased, an increase in kinetic energy is possible if velocity increases. In the case of a decrease in mass and velocity, kinetic energy must decrease because both of the determining factors decreased.