# Dropping an Object of Mass

1. Feb 18, 2014

### ag048744

I have always known that weight is the force of gravity. Yet I have always been confused about one thing. If you hold up an object of mass and drop it, wont the ground experience a force that is greater than when the object just sits there?

2. Feb 18, 2014

### dauto

Yes' temporarily, but the force between the object and the ground is a contact force which has nothing to do with weight or gravity. You get a similar force whenever you lean against a wall, in which case the contact force isn't even vertical and clearly unrelated to your weight.

3. Feb 18, 2014

### StefanT

When the object just sits there on the surface of the earth the force experienced by object onto the earth, and the earth onto the object is equal and opposite in direction and it depends on the objects distance from the centre of the earth. The force of gravity causes the object to exert a force onto the earth, the earth exerts an equal force opposite in direction on the object called the normal force. These two forces are balanced, therefore there is no net force, resulting in no acceleration.

When you set something into free fall from a certain height, it will accelerate toward the earth based on the force of gravity and given enough time will reach terminal velocity due to drag, because the force of gravity will be balanced by the drag of the air on the object causing it to stop accelerating. When the object finally hits the earth, the force exerted temporarily onto the earth, will also be exerted by the earth on the object, and will be based on the objects change of momentum required to provide the reverse acceleration settling it onto the surface of the earth. This force is called the impulsive force, a large force which occurs during collisions over a small period of time. After this impulsive force settles the object onto the earth and ceases it from further accelerating, we return to the scenario in the first paragraph.

TLDR: Yes and the reason that the force experienced is greater on impact is because if the object was 1kg and travelling at 20 m/s, a force of 20 N will be exerted on it, in say one second, to bring it to 0 m/s. While just on the ground the object exerts a force of 9.8 N. This is the basic idea and my understanding of it.

Last edited: Feb 18, 2014