Mechanical Concepts Learning Objectives: To be able to define the key terms regarding mechanical concepts. To be able to calculate velocity and acceleration. To be able to explain Newton’s three laws in a sporting context.

The Physics of Sprinting 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’. 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) Start0000 ÷ 0 = = ÷ 1.7 =

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’. What does the graph tell you in terms of what energy sources are used during the 100m sprint?

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) Start0000 ÷ 0 = = ÷ 1.7 = = ÷ 1.2 = = ÷ 1.1 = = ÷ 1.0 = = ÷ 1.0 = = ÷ 1.1 = = ÷ 1.2 = = ÷ 1.3 = = ÷ 1.4 = = ÷ 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 = ( ) ÷ 1.1 = 0.69m/s Units are m/s, i.e. for every metre covered the athletes velocity increases by 0.69m/s.

Vectors and Scalars Scalar: a quantity that has a single dimension, magnitude. Vector: a quantity that has two dimensions, magnitude and direction. Vectors are usually represented by arrows, which can show direction, line of application, point of application and (sometimes) magnitude.

The Basic Concepts behind Newton’s Laws Forces Forces are what change a body’s state of motion. Forces are the ‘push’ or ‘pull’ that one body applies to another. Definition: a force is that which alters or tends to alter a body’s state of rest or uniform motion in a straight line. There are two types of force: Internal forces – those that we generate ourselves, through contraction of muscles. External forces – from outside our body, such as air resistance, gravity and contact with the ground or another body. Forces are vectors.

Gravity Weight is a force. It is the effect of gravity on a body. Mass is the quantity of matter. Weight is mass x gravity. Friction Whenever one object moves or tries to move over another friction occurs acting parallel to the surfaces in contact and opposing the movement. This plays a key role in most sports. Air Resistance Air resistance is friction due to air passing over surfaces. Inertia The reluctance of a body to change its state of motion.

Homework Newton’s Laws Write one page of A4. Half a page to describe each of Newton’s laws in your own words and half a page to explain these laws in a sports context of your choice.