Transcript here
Characteristics of Motion What is motion ? What are the different types of motion? What is motion??? When a body is continuously changing its position with respect to the surroundings , then we say that the body is in motion. Types of Motion • Linear Motion • Angular/rotary Motion • General Motion • Projectile Motion Linear Motion Motion that occurs in a straight line. All parts of the body move in the same direction and at the same speed. e.g. an athlete running a 100 meter race along a straight track is said to be a linear motion. Angular/Rotary Motion A body is said to be in rotary motion when it stays at one place and turns round and round about an axis. example :a rotating fan, a spinning top, the earth. General Motion • A combination of angular motion and linear motion. It is the most common form of motion, as most human movement requires the rotation of body parts around joints • Example, a racing cyclist uses a combination of several angular motions to produce the linear motion of the bicycle. Projectile Motion • As soon as an object is thrown it becomes a projectile and is influenced by the principles that govern projectile motion – gravity, air resistance, speed, height and angle of release. • Projectiles can include anything that is in the air, i.e rugby balls, shuttle coxs, frisbees etc. Speed, Height and Angle of Release • Different angle of release affects the distance travelled and the height attained by an object. When a ball is released from ground level, the optimal angle for release for maximum distance is about 45 degrees. Air Resistance • Air resistance affect objects in motion by slowing them down. As a body moves through the air, a force is created which tries to resist or stop the movement. This force when an object moves through the air is called drag. The faster a body travels, the greater the drag. The Bernoulli Principle The Bernoulli Principle is perhaps the most vital idea of physics with regards to flight. The principle states that viscous fluids – such as air – tend to follow curved surfaces. Because air has minimal interference with the movement of curved surfaces, such movement creates minimal air pressure. Conversely, if air does not have a curved surface to follow, air pressure is created. As demonstrated in the above sketch, a frisbee has a curved surface on the top, and an angular surface on the bottom. So when it passes through air, it creates high air pressure on the bottom, with low air pressure above. According to the Bernoulli Principle, high pressure has more force than low air pressure. So, the high pressure works as a cushion against gravity, creating lift and thus flight. Frisbees also have a large circle of ridges on its top. These ridges are used to create a microscopic amount of turbulence, which makes the air stick to the top. This creates stability. Centre of Gravity What is gravity ? How does it affect our balance? Centre of Gravity • Is the centre point of a body’s mass, the point about which all parts are equally balanced. In the body the C.O.G passes between the Ilium and forward of the sacrum Determining the Centre of Gravity Box Method Where you draw a box around the object and draw diagonal lines in the shape of an X inside the box, the point at which the two lines cross is the COG. LINE OF GRAVITY An imaginary vertical line which passes through the center of gravity. BASE OF SUPPORT The area within an objects point of contact with the ground. The larger the area the base of support covers, the more stable an object will be. STABILITY • Balance is reached when the LOG falls through the BOS. Stability Balance is reached when the LOG falls through the BOS. Balanced Unbalanced Applying Stability Stability is vital to any movements. It is improved through: 1. Widening the base of support 2. Lowering the centre of gravity 3. Keeping the line of gravity within the base of support Stability also allows a person to move quickly, as a stable base is able to be used by muscles more effectively in order to initiate movement LOG & BOS IN PHYSICAL ACTIVITY • The LOG must go outside of the base of support to initiate or continue movement. The direction the line of gravity takes relative to the base of support will be the direction of movement. The further away the line of gravity is from the BOS the greater the tendency the body has to move in that direction • E.G. Evasive running, Sprinter start position Applying the Theory of Balance Why does this not fall over? Because the centre of gravity and therefore line of gravity falls inside the base of support Sports Field • How can you use the principal of balance/stability in ultimate Frisbee? Question: What is a lever? • Levers are simple machines made up of a pivot point and an arm. Levers help apply force as they can move greater loads with a set amount of force. Levers also help move loads at greater speeds. The amount of leverage a person possesses is dependant upon the length of their body (particular the length of their arms). 1. 2. Longer levers result in greater speed, beneficial for throwing and striking Short levers results in greater strength, beneficial for pushing, pulling and lifting objects Levers consist of 3 parts Resistance Effort or Force Fulcrum (pivot) Levers Force Arm (FA) The distance from where a force is applied to the fulcrum. Resistance arm (RA): The distance from where a resistance acts to the fulcrum First Class Levers A First-Class Lever is a lever in which the fulcrum is located in between the Effort/Force and the load. Working First Class Levers Other Examples Second Class Lever A second class lever is when the fulcrum is at one end and the load is between the fulcrum and the effort. Working Second Class Levers Third Class Lever In the third class lever, the resistance is at one end, the force is at the middle, and the fulcrum is at the other end. Working Third Class Levers Other Examples What lever is used in the Forehand? What lever is used in the Forehand? FULCRUM LOAD Newton’s Law’s of Motion ‘An object at rest will stay at rest, and an object will stay in motion at constant velocity, unless acted upon by an unbalanced force’ What does this mean? This means that there is a natural tendency of objects to keep on doing what they’re doing. All objects resist changes in their state of motion. In the absence of an unbalanced force, an object in motion will maintain this state of motion NewtoN’s Law’s of MotioN How can this law be manipulated to give benefits in sport? This means that to stop something we need to apply some sort of force, the greater the momentum and weight of an object the greater the force required to stop it. Faster & larger someone is the harder it is to stop them i.e Jonah Lomu NewtoN’s 1st Law of Motion in Ultimate What about in Ultimate? In ultimate the Frisbee is constructed with heavier edging to help overcome the inertia and external forces trying to stop it. Also the faster rotation on it, the more it breaks the friction/drag attempting to stop it NewtoN’s 2nd Law ‘When a force acts upon a mass, the result is acceleration of that mass’ What does this mean? Everyone unconsciously knows the 2nd law. Everyone knows that heavier objects require more force to move the same distance as lighter objects. NewtoN’s 2nd Law Cont. Mass x Acceleration = Force How can we apply this in Ultimate? By applying more force/speed to the Frisbee the harder it is for the opponent to stop it, and the further the throw will go. Force can be applied by rotation and power. NewtoN’s 3rd Law ‘For every action, there is an equal and opposite reaction’ What does this mean? This means that for every force there is a reaction that is equal in size, but in the opposite direction. That is to say that whenever an object pushes another object it gets pushed back in the opposite direction equally hard. NewtoN’s 3rd Law Cont. How does a Frisbee fly then? The Frisbee has been specifically shaped to create updrafts to help it fly. The Frisbee is shaped with a curved top to help create air flow over it and then down, while its bottom is created with an indent, this allows air to circulate into it. The circulation creates updraft, hence pushing the Frisbee upwards. Force Summation What is Force Summation? Force summation is the correct timing and sequencing of body segments and muscles through a range of motion. To gain maximum momentum, the force needs to be generated by: • • • • Using the as many segments of the body as possible In the correct sequence, large to small muscles Correct timing Through the greatest range of motion Example of Force Summation For example, like in a shot put throw, the larger muscles (quadriceps) are required to flex the knee, then the energy is moved through to the gluts to extend the leg. Before energy is lost from a muscle group, the next largest comes, creating max force. The energy is then moved to the abdominals, the pectorals, then finally the biceps to give the shot put a forceful throw. Correct sequence of a Forehand