Angular Motion

Angular Motion

Centre of mass

Levers

Torque

Axes of rotation

Centre of mass

Centre of mass is the point where the weight of an object acts equally on both sides. It also known as the centre of gravity. The position of an object's centre of mass varies depening on its size and shape.

The lower to the ground you are the more stability you will have. You can gain more stability by bending your knees to lower your centre of mass. Having a wider base of support means that more force is required to knock you off balance. If someone’s line of gravity falls outside their base of support this means that they are relatively unstable. If the line of gravity falls within the objects base of support they have more stability.

The Fosbury Flop improved performance in high jump as athletes could jump over higher bars by changing their centre of mass. When performing the Fosbury Flop athletes move their centre of mass outside their body and under the bar. This allows the athlete to jump over the bar at a higher height when arching their back. Whereas before jumpers used the western roll technique which involved them having to lift their centre of mass over the bar which required more effort resulting in them not being able to jump as high.

The gymnast is able to move his centre of mass when rotating around the bar. After reaching the lowest point, he bends his legs up which moves his centre of mass a bit closer to the centre of rotation. As the centre of mass is moving in a circle the athlete needs to use his muscles to generate a force to pull it towards the centre of rotation to maintain stability.

Messi naturally has a lower centre of mass compared to other footballers due to his height which is around 1.69m. He makes it lower when dribbling as a lower centre of mass will allow him to have better balance, coordination and weight shift ability. To do this he drops his shoulders, hips and trunk to lean forward so that his centre of mass lowers. As he gets low the opposition are higher so they have less stability than he does so he has more chance of getting the ball off them.

Levers

Muscles, bones and ligaments work together to produce movement through mechanisms called lever systems. A joint forms the axis/ fulcrum, the muscles apply the force/ effort to move the object and anything its holding which acts as the weight/resistance.The functions of levers allow athletes to increase the resistance that they can move, increase speed or increase the mechanical advantage of a movement which means that they don't have to produce as much effort to produce the movement. In a lever, if the distance from the effort to the fulcrum is longer than the distance from the load to the fulcrum, this gives a greater mechanical advantage.Levers help us do work more efficiently by allowing us to lift more or move faster. 1st & 2nd class levers are very efficient, especially when the loads are located close to the fulcrum while efforts are further from the fulcrum. The efficiency of 1st & 2nd class levers decreases when loads move further from the fulcrum. Whereas 3rd class levers are the least efficient. The majority of muscle-joint system levers in our body are 3rd class levers. Efficiency can be increased by moving the load closer to the fulcrum.

Second class levers is where the load is between the fulcrum and effort. Second class levers have the most mechanical advantage meaning that they are able to move the most load with the least effort.

Third class levers is where the effort is between the fulcrum and load.

First class levers is where the fulcrum is between the load and effort.

The athlete is using the second class lever when jumping to take the shot. The lever is found in the ankle area. When standing on his tiptoe, the ball of the foot acts as the fulcrum, the weight of the body acts as the load and the effort comes from the contraction of the gastrocnemius muscle. ​

The athlete is using the first class lever when doing a tumble turn. The swimmer has to tuck her head in by looking downwards. The lever is found in the vertebrae area. When turning the neck as the fulcrum, the head acts as the load and the effort comes from the contraction of the muscles in the neck.​

The athlete is using the third class lever when extending her knee. The lever is her leg with the fulcrum at the knee. The load is at the foot and the effort is from the pelvis.

Centre of mass & Levers

When performing on the still rings gymnasts must remain still. To do this the gymnast must keep the centre of mass of his body and the rings under the pivot point of the cables that the rings are attached to. If his centre of mass isn’t directly under this point the gymnast will begin to swing and find it more difficult to remain stationary.

When on the beam a gymnast must use her legs to exert a force onto the beam to lift her body off it. The force compresses the beam resulting in a spring effect. The beam then exerts a force onto the gymnast allowing her to move up into the air to perform her jump. Centre of mass is normally around a gymnast’s hips. When standing still on the beam gymnasts can remain stable as their centre of mass is above the beam meaning gravity is pushing her down onto the beam. However when the gymnast begins to shift her weight her centre of mass will move slightly. When the gymnast starts to perform flips the gymnast’s centre of mass will not be under the beam anymore. The body will then start to act like a lever and the more she leans the more torque is generated. To combat the torque the gymnast has to realign her centre of mass which can be done by squatting downwards so that her centre of mass can be lowered to regain stability and her balance. Forces - The Physics Behind the Balance Beam (2021).

The fulcrum is at one end of a second class lever and the applied force is at the other, and the load that is to be moved is between them. This lever causes the load to move in the same direction as the force being applied. If the load is closer to the fulcrum than the effort less effort will be required to move the load which will increase performance as athletes won't fatigue as quickly as lesseffort is being used to perform each movement. The gymnast is using a second class lever to maintain his position on the rings. The fulcrum is in between the load and effort at the hips, the effort is his feet and the load is his quadriceps. Therefore the athlete is using both his centre and mass and the lever system to increase his performance by being able to stay still for longer.

The hip is the fulcrum, the back is the effort and the weight on the shoulders is the load in this back squat. This is a third class lever system. This lever is inefficient because it is a long lever, with the load located as far from the fulcrum as possible. So to make this more effiecient the athlete should change position by leaning forward and moving the weight lower down their back slightly to decrease the length of the lever. This means that the inefficiency decreases. This now allows athletes to lift more weight with the low-bar back squat without having to use more effort to improve their performance. In a lever, if the distance from the effort to the fulcrum is longer than the distance from the load to the fulcrum, there will be a greater mechanical advantage. Therefore, by lowering the centre of mass the athlete is able to have more stability as well as use less effort to squat.

Torque

Torgue is a force that causes an object to rotate. Spins and flips are created by torgue. Twisting force converts linear momentum into angular momentum.

When X- games performers want to spin they have to rotate around an a vertical axis and use the sagittal plane of movement. To double the amount of torgue generated in a spin athletes can twist in the opposite direction than the intended spin. To perform a flip athlete’s must rotate around the horizontal axis. Athletes can also shift their centre of mass higher just as they take off for a flip and by extending their legs they are able to create a longer lever which results in 4% extra torgue per inch.

The term in NFL ‘The low man wins’- highlights that the player who stays the lowest will generate more torgue. Torgue is seen when one player collides into another causing a player to spin. Distance from where torgue is applied is lever. Staying low counteracts torgue. By keeping your centre of mass low you can exert force onto a player who stays high and more likely push them over. Crouch to keep centre of mass low so it is harder for them to rotate. Centre of mass located at hips which lowers when crocuses. As a player rises distance between opponent’s pivot point and his force increases torgue.

Torque

Torgue is a force that causes an object to rotate. Spins and flips are created by torgue. Twisting force converts linear momentum into angular momentum.

When X- games performers want to spin they have to rotate around a vertical axis and use the sagittal plane of movement. To double the amount of torque generated in a spin athletes can twist in the opposite direction than the intended spin. To perform a flip athlete’s must rotate around the horizontal axis. Athletes can also shift their centre of mass higher just as they take off for a flip and by extending their legs they are able to create a longer lever which results in 4% extra torque per inch.

The term in NFL ‘The low man wins’- highlights that the player who stays the lowest will generate more torque. Torque is seen when one player collides into another causing a player to spin. Distance from where torque is applied is the lever. Staying low counteracts torgue. By keeping your centre of mass low you can exert force onto a player who stays high and are therfore more likely to push them over. Players should crouch to keep their centre of mass low so it is harder for them to rotate. Centre of mass is located at the hips which lowers when crouching. As a player rises distance between opponent’s pivot point and his force increases torque.

Axes of rotation

An axis of rotation is an imaginary line in which an object rotates around. There are three axes of rotation these include vertical axis, sagittal axis and transverse axis.

The vertical axis goes down the body from the head to the toes and separates the body into a left and a right side. In addition, it is formed by the intersection of the sagittal and frontal planes of movement. When a figure skater spins but keeps one foot on the floor in the same spot she is rotating around the vertical axis.

The transverse axis splits the body into the top and bottom halves. It passes horizontally from left to the right. In addition, it is formed by the intersection of the frontal and transverse planes of movement. When a diver performs a front somersault as part of a dive she is rotating around the transverse axis.

The sagittal axis divides the body horizontally from the front to the back. In addition, it is formed by the intersection of the sagittal and transverse planes of movement. When a gymnast performs a cartwheel as part of her floor routine she is rotating around the the sagittal axis.

Bibliography

(2021) Youtube.com. Available at: https://www.youtube.com/watch?v=-5epz2jAIEU (Accessed: 23 March 2021).Basic Biomechanics: Moment Arm & Torque (2021). Available at: http://www.aaronswansonpt.com/basic-biomechanics-moment-arm-torque/ (Accessed: 23 March 2021). Physics Of Gymnastics (2021). Available at: https://www.real-world-physics-problems.com/physics-of-gymnastics.html (Accessed: 23 March 2021). Allain, R. (2016) How Olympic Gymnasts Use Physics to Pull Off Those Crazy Twists, Wired. Available at: https://www.wired.com/2016/08/physics-behind-every-olympic-gymnasts-twist/ (Accessed: 23 March 2021). Physics In Gymnastics (2021). Available at: https://prezi.com/bg1limfpuwy6/physics-in-gymnastics/?fallback=1 (Accessed: 23 March 2021). Anatomy of Levers, Part 6: Lever Efficiency (2021). Available at: https://www.crossfit.com/essentials/anatomy-of-levers-part-6-lever-efficiency (Accessed: 25 March 2021). Anatomy of Levers, Part 6: Lever Efficiency (2021). Available at: https://www.crossfit.com/essentials/anatomy-of-levers-part-6-lever-efficiency (Accessed: 26 March 2021). (2021) Ocr.org.uk. Available at: https://www.ocr.org.uk/Images/524161-biomechanics-teacher-guide.pdf (Accessed: 26 March 2021). Forces - The Physics Behind the Balance Beam (2021). Available at: https://sites.google.com/site/physics100project/forces (Accessed: 10 May 2021).