Newton's second law
A team's tackling can make or break any game of rugby. And part of being good at tackling is overpowering your opponent with the force you hit them with. According to Newton's 2nd Law, the force of a player hitting another player can be found my multiplying his mass by his acceleration. F=ma
This means if you double the mass, you double the force. Similarly, if you double the acceleration, the force is doubled. This explains how a player running full speed can be knocked back when hit by a defensive player. It depends on how much force the tackler can generate, by exploding forward as fast as he can. This is his acceleration!
This means if you double the mass, you double the force. Similarly, if you double the acceleration, the force is doubled. This explains how a player running full speed can be knocked back when hit by a defensive player. It depends on how much force the tackler can generate, by exploding forward as fast as he can. This is his acceleration!
Scenario 1 below shows a typical standoff between two wingers (with average masses of a winger, 80kg). The one on the left is running with the ball and the one on the right is tackling. The reason the tacklers acceleration is higher is because he is allowing the offensive player to approach him, waiting to explode, practically jump, straight at him with full force. Therefore he will have a greater force and will be able to overpower him successfully.
|
And this is where superstars come in... Scenario 2 displays the same play but with a different offensive winger, Jonah Lomu, the beast! At 130kg, he still has the speed of winger which gives him the ability to completely dominate outside on the wing. Even though the defense man has greater acceleration, Lomu's mass gives him a greater force. This gives him the ability to break through tackles.
The video to the right displays how he uses his mass to his advantage to generate a greater force than his defenders, and literally run them over. (0:43 seconds: great example) |
|
Newton's First Law
Newton's First Law, Law of Inertia, can easily be explained through a kick. This law states that an object will stay at rest or at constant velocity until acted upon by an unbalanced force. Before the kick, the ball is still and will stay still forever until acted upon by an external force, like a foot striking it. But even after the strike, the law is still in play. The ball would've continued to project in the direction it was kicked, if not for an unbalanced force: gravity. It's horizontal speed stays constant, since no force is resisting it, but it is constantly being acted upon by the force of gravity. And so the ball will continue it's parabolic path until, again, it is acted upon by a force such as a player. A player catching the ball would apply a force equal to its horizontal and vertical forces but in the opposite directions, completely stopping the ball from moving.
Newton's Third law
Newton's Third Law, states that for every force, there is an equal and opposite force being exerted. Although nobody ever really thinks about it, how would you explain how a rugby player runs forward? Most would say that he pushes himself forward off of the ground, right? But that isn't entirely correct. How it really works is that the player pushes down on the ground with a force, but that doesn't make him go forward, that actually moves the earth down (an infinitely small amount). What propels him forward is the equal, opposite force that the earth puts back onto him. The earth pushes back on the player, which in turn, moves him. Although the player moves a lot more than the earth due to the difference in masses, the forces they exert on each other is equal.