Linear motion Angular motion Biomechanics Linear motion Angular motion

Linear Motion Speed refers to how fast an object is moving. It is a scalar. Avg speed in metres per second (m/s) = Distance covered Time Taken So, a 100m sprint run in 15s: Avg speed = 100 = 6.67 (m/s) 15

Velocity is a similar concept to speed but includes ‘direction’ Velocity is a similar concept to speed but includes ‘direction’. It is defined as the rate at which an object changes its position. (if I clapped my hands rapidly they would be moving at great speed but at zero velocity, as they are always moving back to the same position) As ‘direction’ is also involved, velocity is a vector. Distance is replaced with the concept of displacement. Displacement is the shortest straight line between the starting and finishing point. Therefore: Avg Velocity = Displacement Time

Avg Velocity for 100m Sprint Timing Point (displacement in metres) Distance Covered (mtrs) Time to reach this point (secs) Time taken for this 10m section (secs) Avg velocity for each 10m section (displacement/time) Start 0 ÷ 0 = 0 10 1.7 1.7-0.0 = 1.7 10 ÷ 1.7 = 5.88 20 2.9 30 4.0 40 5.0 50 6.0 60 7.1 70 8.3 80 9.6 90 11.0 100 12.6

Task Calculate time taken for each section. Use this to calculate avg velocity for each section. Draw a graph with displacement along the ‘x axis’ and velocity along the ‘y axis’. (see next 2 slides for graphs info) What does the graph tell you in terms of what energy sources are used during the 100m sprint?

Velocity-Time Graphs A velocity-time graph can be used to show the velocity of an object. Distance is on the y axis and time is on the x axis The blue line is steeper and shows greater acceleration (it is increasing its velocity at a greater rate than the blue line) When the red line is horizontal it shows a constant velocity (of 8m/s) At 7s the red line is sloping downwards showing that the object is slowing down until on 10s its velocity is again zero.

Avg Velocity for 100m Sprint Timing Point (displacement in metres) Distance Covered (mtrs) Time to reach this point (secs) Time taken for this 10m section (secs) Avg velocity for each 10m section (displacement/time) Start 0 ÷ 0 = 0 10 1.7 1.7-0.0 = 1.7 10 ÷ 1.7 = 5.88 20 2.9 2.9-1.7 = 1.2 10 ÷ 1.2 = 8.33 30 4.0 4.0-2.9 = 1.1 10 ÷ 1.1 = 9.09 40 5.0 5.0-4.0 = 1.0 10 ÷ 1.0 = 10.00 50 6.0 6.0-5.0 = 1.0 60 7.1 7.1-6.0 = 1.1 70 8.3 8.3-7.1 = 1.2 80 9.6 9.6-8.3 = 1.3 10 ÷ 1.3 = 7.69 90 11.0 11.0-9.6 = 1.4 10 ÷ 1.4 = 7.14 100 12.6 12.6-11.0 = 1.6 10 ÷ 1.6 = 6.25

Energy Sources used during 100m Sprint Phosphocreatine (PC) is used as an energy source to resynthesise ATP. PC stores provide energy for 5-8s of maximal exertion. Velocity begins to decrease when PC stores run out. The body then predominantly uses the lactate anaerobic system to resynthesise ATP. This system is slower to resynthesise ATP as it involves many more chemical reactions, therefore less force can be exerted by muscles and the sprinter slows down.

Acceleration and Deceleration Avg Acceleration (m/s) = final velocity – initial velocity time Use this to calculate the sprinters acceleration between 20m to 30m. Initial velocity (after 20m) is 8.33m/s Final velocity (after 30m) is 9.09m/s Time taken to run this section is 1.1s. Therefore acceleration = (9.09-8.33) ÷ 1.1 = 0.69m/s² Units are m/s², i.e. for every metre covered the athletes velocity increases by 0.69m/s².

Angular Motion Angular motion is about something that is rotating, such as a diver or gymnast somersaulting.

The Body in Rotation Angular Velocity Some Key Terms: Angular Velocity Angular Acceleration Angular Momentum Moment of Inertia Conservation of angular momentum The rate of movement in rotation The rate of change of velocity during angular movement The amount of motion that the body has during rotation (angular velocity x moment of inertia The resistance of a body to change of state when rotating The principle that the angular momentum of an object remains constant as long as no external force (moment of torque) acts on that object

Levers and Moments The amount of turning force that is generated by a resistance is known as the torque or moment of force. Moment = resistance x distance from axis This is known as the moment arm and is either a resistance arm or an effort arm. This is why an object seems heavier when you hold it further from your body

Angular Movement Angular momentum is the amount of motion a body has when rotating. Angular momentum = angular velocity x moment of inertia (remember moment of inertia = mass x distance from axis) Angular moment follows Newton’s first law (which in this case is known as the ‘conservation of angular momentum.’ A body will continue spinning unless a force (e.g. air resistance, friction) acts on it.

Moment of inertia = mass x distance from axis A body cannot change its mass during a movement but can its distance from axis of rotation. If mass moves closer to the axis (tuck) then moment of inertia decreases. If moment of inertia decreases then angular velocity must increase. Youtube example

Biomechanics British gymnast Beth Tweddle won the 2009 World Championship Floor Exercise title. Her routine involved a series of powerful tumbling sequences, balances and rotational movements, one of which is shown below. Explain how a gymnast can alter the speed of rotation during flight. (7 marks)

Mark Scheme A. Changing the shape of the body causes a change in speed B. Change in moment of inertia leads to a change of angular velocity/speed/spin of rotation/ angular moment; C. Angular momentum remains constant (during rotation) D. Angular momentum = moment of inertia x angular velocity E. Angular momentum - quantity of rotation/motion F. Angular velocity - speed of rotation G. Moment of inertia - spread/distribution of mass around axis/reluctance of the body to move H. To slow down (rotation) gymnast increases moment of inertia I. Achieved by extending body/opening out/or equivalent J. To increase speed (of rotation) gymnast decreases moment of inertia K. Achieved by tucking body/bringing arms towards rotational axis

Calculate the ‘moment of force’ at the knee in both exercises Calculate the ‘moment of force’ at the knee in both exercises. You must show your working. (i) Front squat (2) (ii) Smith machine squat (2)

Using ‘Newton’s First and Second Laws of Motion’, explain how the swimmer dives off the starting blocks. (4 marks)

Mark Scheme A. Force is applied by the muscles Newton’s First Law of Motion/Law of inertia B. Performer will remain on the blocks unless a force is applied C. Performer continues to move forwards with constant velocity until another force is applied D. Water slows the swimmer Newton’s Second Law of Motion/Law of Acceleration E. Mass of swimmer is constant F. Greater the force exerted on the blocks, the greater the acceleration/momentum G. Force governs direction