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Biomechanics Laws Today’s session will cover Newton’s laws of motion. First Law – Inertia Second Law - Acceleration & Momentum Third Law - Equal & Opposite Newton’s First Law An object at rest tends to remain at rest unless acted upon by some external force. Known as Inertia. Basically inertia is an objects resistance to move. Which is harder to move? Having a great deal of inertia can be advantageous in some sporting situations. How? If you have a lot of inertia you can be difficult to move. E.g. a rugby scrum, wrestling, judo Of course having a lot of inertia has disadvantages as well in sporting situations. How? If you have a lot of inertia you require a lot of force or effort to get you moving. It can also mean decreased agility. Newton’s Second Law When a force acts upon a mass, the result is acceleration of that mass. Student example Force = Mass x Acceleration F = MA If each is hit or bowled with the same amount of force, which one accelerates the most? Why? The table tennis ball because it is lighter. If the tennis ball is hit with gradually increasing force, what happens to its acceleration? The acceleration will increase with increasing force. Summary of 2nd law The greater the force, the greater the acceleration. The smaller the mass, the greater the acceleration when a constant force is applied. The mass will accelerate in the direction the force is applied. How could you apply Newton’s 2nd law in a sporting situation. Newton’s Third Law For every action, there is an equal and opposite reaction. “What goes up, must come down” Summary of 3rd law When we apply a force to something, this is known as a action force. The object we apply a force to, applies a force back, a reaction force. What other example of this can you think of? When a ball is bounced, it bounces back in a direction opposite to that in which it was dropped. If these forces are equal, why is the earth not pushed backward when we drive out of the starting blocks in a 100 metre race? The earth has a huge mass and therefore huge inertia. We cannot generate enough force to overcome this inertia.