F = ma

Up Players and Forces Interactions Newton's third law F = ma Net Force

Unbalanced forces cause acceleration. 
If all the forces acting on a player do not balance, then a net force is acting on the player.

A net force acting on a player changes the velocity of the player.
The direction of the acceleration is the direction of the force.

A net force acting on an object at rest causes the object to move.


For a short time the kicker exerts a force on the ball causing it to accelerate from rest.		 A net force pointing in the direction of the velocity causes the object to speed up.

The ground pushes the player forward, causing him to speed up.		 A net force pointing opposite to the direction of the velocity causes the object to slow down.

The receiver exerts a force on the ball opposite to the direction it is moving, thus slowing it down and catching it.

A net force pointing perpendicular to the direction of the velocity causes the object to turn.

The ball carrier is turning trying to avoid a tackle.  The ground pushes him towards the inside of the turn.

Larger net forces produce larger accelerations.
But the rate at which the velocity changes also depends on the mass of the object.

F = ma

Same force, larger mass  ß à  Smaller acceleration
IIn the pictures shown above, the players probably have similar masses. 
During the collisions, they exert forces of similar magnitudes on each other. 
Their accelerations have similar magnitudes. 
That does not necessarily mean that their final speeds will be nearly equal. 
We have to add the changes in the velocity produced during the collision to their incoming velocities to find their final velocities.