Object Mass

• Mass refers to an object's matter (bulk) and its inertia level, according to the Encarta Encyclopedia. Unlike weight, mass also applies to objects in places that don't experience gravity, such as outer space. Greater mass on the part of the object will boost the impact strength. For example, an empty polystyrene foam cup contains mostly air and has little mass, so it produces little impact when it falls to the ground. Howeer, a glass cup full of ice will have an impact with much greater strength at the same speed due to its larger mass.
  
  

Object Speed

• The speed of the moving or falling object also affects the strength of the impact. Speed can even make objects with little mass dangerous. In addition to movement created by the object itself, various external factors can increase or decrease its speed. A metallic object will move faster as it approaches a magnetic surface, boosting the strength of impact. Gravity levels also change the rate at which things fall. A human on the Moon will fall at a slower speed and have less impact than a human falling from the same height on Earth. An aerodynamic object will fall more rapidly.
  
  

Surface Speed

• If the surface the object hits also remains in motion, the strength of impact may increase or decrease, depending upon the movement direction. When two objects collide at similar speeds, moving in the same direction, they create less of an impact than one object hitting a stationary surface or an object moving in the opposite direction. These factors heavily influence the strength and severity of train and automobile collisions. When struck by a car moving at 40 mph, an automobile traveling at 35 mph will not receive as much damage as a parked vehicle.
  
  

Surface Movement

• When the surface struck by an object can move, the strength of the impact isn't as great. For example, a sign post or a flimsy fence will give way to an impact more easily than a large tree. Also, for some objects, it depends upon which side something strikes them. When hit from the front or back, a shopping cart moves with less difficulty compared to when something hits it from the side.