Brownian motion in Rugby
The number one rule as a rugby player is to “RUN STRAIGHT” towards the try zone. But when you’re running and people are trying to tackle you stiff-arm them.
When this happens the player does not go down in a tackle but merely is randomly slightly changed in direction. Therefore, this could be considered to be Brownian motion because the player’s trajectory and speed depends on what opposing person she will bounce off.
However, if she is tackled, depending on her force and the opposing force she could go down to the ground.
So lets say our biggest player who is about 80 kg is accelerating at 3 m/s2 is about to get tackled by the opposing players fullback who is probably 60 kg and running at 4 m/s2, will she get beat?
F1=(80kg*3m/s2) and F2= (60kg*4m/s2)
F1= 240N F2= 240N
Therefore, if they hit each other both face on neither would bounce off and fall to the ground.
However, in a tackle you are supposed to bend low and tackle their hips. Therefore, by being below their center of mass the same amount of force will rotate the player and will be able to move the player to the ground.
If the opposing player tackles a quarter meter away from our player’s center of mass she will probably be able to tackle our player to the ground.
Her torque would be
T= 0.25m *(240N)*sin (90)