Biomechanics 5
Kinematics 2
Projekt: Cizí jazyky v kinantropologii - CZ.1.07/2.2.00/15.0199
Daniel Jandačka, PhD.

Velocity
When we say that somebody is slow or fast we are actually describing his/her velocity
In biomechanics one of our tasks is to quantitatively describe velocity.
If a property is quantifiable, it means that certain aspects of such property are measurable and
can be expressed by a number.
http://www.extreme-sports.cz/Public/Images/News/651e965f388b9551db179490a00c36d6.jpg

Mean Speed
C:\Jandys\KTV\Biomechanika\Prezentace_Brno\Biomechanics
Presentation\book-1\book-1\images\17\eq01.png
Mean speed v is the distance s divided by time t taken to cover the distance
Mean speed is important in describing performance in many sport events. In the events where
athletes must cover the same distance their speed is the direct measure of their success.
In cross country skiing, for example, the winner covers the given distance in shortest possible
time. The mean speed of an athlete is the distance he/she covers divided by his/her final time.
http://www.crosscountryskier.com/cross_country_ski_images/SeanHalsted_JamesNetzPhoto.jpg
The SI unit is metre per second (m/s).

•Mean speed, however, does not say much about the actual course of the race. We know nothing about
their maximum speed and about those sections of the track where racers speeded up or slowed down.
Table Split times and mean speeds of pacemaker in sections 1-5, 10-15, 20-25, 30-35 and
40-marathon, to make the final time of 3 hours.
Distance covered (m)
Split time (hod:min:s)
Section mean speed (m/s)
1 000
4:28
3,73
5 000
22:20
10 000
43:50
3,94
15 000
01:05:00
20 000
01:25:10
3,90
25 000
01:47:30
30 000
02:09:00
3,97
35 000
02:30:00
40 000
02:51:30
4,17
42 125
03:00

Instantaneous velocity
•Instantaneous velocity is the velocity of a moving object at a particular instant of time. It is
the velocity attained by the object in a very short period of time (approaching zero).
For example - release velocity
Instantaneous velocity is vector quantity

Mean and standard deviation of the kicking toe’s velocity (n = 9): The solid, dashed, and dotted
lines represent the mean for kicks when starting from the 0°, 45°, and 90° stance positions,
respectively. The solid area represents the standard deviation from the 45° curve.
Magnitude

Displacement Velocity
•The displacement divided by the length of the time interval
In downhill skiing, for example, we are not that interested in mean speed but rather in
displacement velocity, i.e. how fast skiers moved from start to finish, regardless the actual speed
of going around gate poles
https://encrypted-tbn2.google.com/images?q=tbn:ANd9GcTs8EG9O3mIud540zYdhdBYsuisDHSZwCB1mewtQuiAfW2c
9Egb-A http://i.ytimg.com/vi/ECWF8dI0T2o/0.jpg

Importance of Speed
•There are many sport events in which the winner is the competitor with the highest mean speed.
•
•Speed is also important in sport events where it is only one of the factors influencing the
overall performance.
Let us have a look at tennis serve. After a good serve the ball flies with the speed of 100 - 200
km/h and it is really difficult to come up with an equally good return. Why? The faster the ball
flies the less time the opponent has to move. For example Ivan Karlovič is able to serve with the
record speed of 251 km/h (70 m/s). The distance between the opponents is about 24 m. How much time
does the opponent have to react to Ivan Karlovič’ serve?

The opponent has only about 0.3 second for a motor task of precisely returning the ball. We can see
that in tennis the speed of the ball determines the time players have to manage a stroke or to move
to a desired position.
In the same way in sports such as football, floorball, hockey, and handball the speed of a flying
projectile is important for goal keepers because it determines the amount of time they have to
catch it.
Speed is also a positive factor of performance in long jump, triple jump, high jump, and ski
jumping.
Gymnasts need high speed in vault so that they can manage the given number of rotations.
time = displacement / speed
time = 0.34 s

Thank you for your attention
Projekt: Cizí jazyky v kinantropologii - CZ.1.07/2.2.00/15.0199