Re: Why are bigger people harder to tackle

Momentum is the concept you are looking for.  The following web reference, 
found with a search for the term

    momentum

describes momentum.

    http://encarta.msn.com/find/Concise.asp?z=1&pg=2&ti=761554136

Momentum is the product of mass and velocity.  When you try to tackle a running 
football player, the player's momentum is directly proportional to their mass.  
The more massive, the more momentum, more player's running at the same velocity.

Since the momentum is simply a product of mass and velocity, a more massive 
player is easier to tackle before they get up to speed.  If you are a really 
light but fast tackle, you might also suspect it possible to upset a heavier 
player by tackling from the rear.

Most high school physics textbooks include a more complete discussion of 
momentum.

Thanks for your question.

sid