EDU4SBM Sports Biomechanics 1 Lecture Week 3 Force Production, Forces, COG, Inertia, Impulse

EDU4SBM Sports Biomechanics 2 Force Production A force is a push or pull that changes, or tends to change the shape or the state of motion of an athlete or object Force can:  Change the direction of a moving object  Change the speed of a moving object  Balance another force to keep an object still

EDU4SBM Sports Biomechanics 3

4

5 Forces Internal forces External forces

EDU4SBM Sports Biomechanics 6 Types of Forces Force without motion – isometric force Force with motion – isotonic force Sub-maximal force Maximal force

EDU4SBM Sports Biomechanics 7 Force without Motion Isometric force Isometric contraction Muscle length does not change Eg:

EDU4SBM Sports Biomechanics 8 Force with Motion Isotonic force Isotonic contraction Muscle length changes Changes the state of motion of the object (body) –Eg:

EDU4SBM Sports Biomechanics 9 Sub-maximal Force Force needs to be at an optimal level for successful performance Sometimes we want less than maximum force –Eg:

EDU4SBM Sports Biomechanics 10 Maximal Force Some activities require maximal force for a higher chance of success This usually happens through combination of a number of forces – force summation

EDU4SBM Sports Biomechanics 11 Force Vectors Vector - means a quantity has direction Force vector - indicates the magnitude and direction of an applied force. Every force vector has a horizontal and vertical component

EDU4SBM Sports Biomechanics 12 Combination of forces to produce a maximal force 2 types –Simultaneously: Eg: high jump take-off, vertical jump for rebound in basketball –Sequentially: Eg: throwing, striking, kicking Force Summation

EDU4SBM Sports Biomechanics 13 Simultaneous Force Summation

EDU4SBM Sports Biomechanics 14 Sequential Force Summation

EDU4SBM Sports Biomechanics 15 Sequential force summation requires the following techniques 1.Use as many body parts as possible 2.Use largest body parts and muscle groups first 3.Sequentially accelerate each body part 4.Sequentially stabilise each body part so the next body part accelerates around a stable base.

EDU4SBM Sports Biomechanics 16 Write down the steps in force summation for a throw from the outfield in softball.

EDU4SBM Sports Biomechanics 17 Centre of Gravity Single segmental objects have their Centre of Gravity directly above the base of support. Sometimes the Centre of Gravity can be found outside the body. (Arc) The balance point of an object

EDU4SBM Sports Biomechanics 18

EDU4SBM Sports Biomechanics 19

EDU4SBM Sports Biomechanics 20 Inertia A bodies resistance to change in its state of motion (either from rest or moving). 1.An objects resistance to beginning motion 2.An objects resistance to changing its state of motion The heavier the object the greater its inertia and therefore the greater force required to move it. Inertia α Mass

EDU4SBM Sports Biomechanics 21 Impulse When a force is applied to an object, the product of the force (F) and the length of time (t) that the force is applied, is called the impulse of the force. Impulse = Ft measured in Newton Seconds.

EDU4SBM Sports Biomechanics 22 The Follow Through in Sport In racket and bat sports, hitters are often encouraged to follow-through when striking a ball. Following through increases the time over which a collision occurs therefore increasing the impulse This contributes to an increase in the velocity change of the ball. By following through, a hitter can hit the ball in such a way that it leaves the bat or racket with more velocity (i.e., the ball is moving faster). In tennis, baseball, racket ball, etc., giving the ball a high velocity often leads to greater success.

EDU4SBM Sports Biomechanics 23 Homework Task Answer the following questions 1. Pick one benefit of biomechanics for a sport of your choice and discuss in detail 2. For the same sport analyse and discuss in detail one form of equipment that has used biomechanics 3. Describe the sequence of body parts in the force summation for a tennis serve