Transcript Document

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)
Start
0
0
0
0÷0=0
10
10
1.7
1.7-0.0 = 1.7
10 ÷ 1.7 = 5.88
20
10
2.9
30
10
4.0
40
10
5.0
50
10
6.0
60
10
7.1
70
10
8.3
80
10
9.6
90
10
11.0
100
10
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’.
• 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)
Start
0
0
0
0÷0=0
10
10
1.7
1.7-0.0 = 1.7
10 ÷ 1.7 = 5.88
20
10
2.9
2.9-1.7 = 1.2
10 ÷ 1.2 = 8.33
30
10
4.0
4.0-2.9 = 1.1
10 ÷ 1.1 = 9.09
40
10
5.0
5.0-4.0 = 1.0
10 ÷ 1.0 = 10.00
50
10
6.0
6.0-5.0 = 1.0
10 ÷ 1.0 = 10.00
60
10
7.1
7.1-6.0 = 1.1
10 ÷ 1.1 = 9.09
70
10
8.3
8.3-7.1 = 1.2
10 ÷ 1.2 = 8.33
80
10
9.6
9.6-8.3 = 1.3
10 ÷ 1.3 = 7.69
90
10
11.0
11.0-9.6 = 1.4
10 ÷ 1.4 = 7.14
100
10
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/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.