Lecture Week 3
Force Production,
Forces, COG, Inertia,
Impulse
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EDU4SBM Sports Biomechanics
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
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Forces
• Internal forces
• External forces
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Types of Forces
Force without motion – isometric force
Force with motion – isotonic force
Sub-maximal force
Maximal force
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EDU4SBM Sports Biomechanics
Force without Motion
• Isometric force
• Isometric contraction
• Muscle length does not change
Eg:
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Force with Motion
•
•
•
•
Isotonic force
Isotonic contraction
Muscle length changes
Changes the state of motion of the object (body)
– Eg:
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Sub-maximal Force
•
•
Force needs to be at an optimal level for successful performance
Sometimes we want less than maximum force
– Eg:
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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
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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
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EDU4SBM Sports Biomechanics
Force Summation
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
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Simultaneous Force Summation
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Sequential Force Summation
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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.
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EDU4SBM Sports Biomechanics
Write down the steps in force summation for a throw from
the outfield in softball.
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Centre of Gravity
The balance point of an object
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)
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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
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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.
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EDU4SBM Sports Biomechanics
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.
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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
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EDU4SBM Sports Biomechanics