E.g. D = S * T and T=D
Example,
A 100m sprinter takes 10s to complete a race. The speed is calculated as follows,
S = 100m/10s
S = 10m/s
However, the velocity is calculated different to the speed because instead of distance being in the formula, displacement is used.
E.g. V = d
T
V = Average velocity
D = Displacement
T = Time taken
The only time speed and velocity can be equal is when an object or someone is travelling in a straight line and in only one direction.
Acceleration
When an athlete increases or decreases velocity, this is known as acceleration. “Acceleration is defined as the rate at which the velocity changes with respect to time”(Hay 1993) Acceleration maybe positive or negative, when a athlete increases their speed it is known as positive acceleration and when they are slowing down it is known as negative acceleration, also called deceleration.
Acceleration can be calculated as the follows,
A = V1 – V2
T
A = Average acceleration
V1 = Final velocity
V2 = Initial velocity
T = Time taken
E.g. A 200m sprinter is running at a pace of 5m/s then accelerates to 10m/s during the last 50m of the race. The calculation can be made to work out the average acceleration of the athlete.
A = 10m/s – 5m/s
50m
A = 5m/s
50m
A = 0.1m/s2
However the sprinters starting velocity is 0m/s at the start of the race.
Vectors and Scalars
Scalars concern elements such as distance and speed, those which can be described in terms of their length, which is known as there magnitude. Displacement, velocity and acceleration come under the vectors heading because, they require both a magnitude and a direction.
Arrows are often used on graphs to represent vectors because they can represent direction and length.
The magnitude of a vector is its size, e.g. 200 is larger than 100. Forceful elements such as pressure, weight, air resistance, friction, mass are all known as kinetic vector quantities. Any quantities without a magnitude and a direction can not be classed as a vector. So, length, speed and volume are all scalar examples.
15.2b Identify the nature and role of friction, gravity and Newtons laws of motion pertaining to sport and exercise
Newton's First Law of Motion:
Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
Newton's Second Law of Motion:
The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors (as indicated by their symbols being displayed in slant bold font); in this law the direction of the force vector is the same as the direction of the acceleration vector.
Newton's Third Law of Motion:
When one object exerts a force on a second object, there is a force equal in magnitude but opposite in direction exerted by the second object on the first
Force
“Force is the push or pull exerted upon an object or body, which may either cause motion of a stationary body or a speeding up, slowing down or even a change of direction of a moving body” (Hay 1993)
Forces are can be generated in many forms. The body can produce its own muscular contractions, however there is various more forces coming from outside our bodies, e.g. gravity, friction, air resistance. If forces were non-existent nothing would be able to move
Friction
Friction is a force that is created whenever two surfaces move or try to move across each other. “A force which always opposes the motion or impending motion, is called friction”(Hay 1993)
There are several factors which effect the force of friction.
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The texture of surfaces, e.g. surfaces can be made of different materials, rough or smooth, and can also be designed in different ways/shapes and patterns to give either more or less friction.
(i.e An ice rink has very little friction, which allows a puck to move across fast and efficiently. To sole of basketball shoes are specifically designed in a certain way to allow a basketball play to have more grip on the court, so they can stop and turn more easily.)
-
Force pushing surfaces together, e.g. Dependant on different pressure pushing the surfaces together can resist the friction. (i.e. The heavier a person skating across the ice the more the friction)
-
The larger the contact force the larger the friction force, e.g. the thicker the wheels on a car, the more friction force there is on the road.
The coefficient of friction can be known as “The ratio of the force needed to overcome friction (Luttgens and Hamilton, 1997)
Friction can act as a negative force and may resist total performance improvement and can also harm.
Friction resists the relative motion between two surfaces within the body.
- Friction is reduced when articulating surfaces are smooth and lubricated
- Joints articulate
- Cartilage is smooth and lubricated by synovial fluid
- Breakdown of smooth surfaces causes wear and tear of joints
- Poor blood supply to cartilage
- Osteoarthritis
Friction can also act as a positive influence to improve performances.
- A frictionless floor, has no force to move, and is also difficult to change horizontal velocity to vertical.
- A normal floor, has friction force and it is easy to change horizontal and vertical velocity.
Friction resists the motion in the direction of travel. The motion of the ball is affected in the positive direction.
Table tennis players can use friction to their benefit. They can hit the ball, by positioning the bat in various angles and at different speeds resulting in spinning the ball., e.g. top-spin, back-spin.
Momentum
