Mechanical Effect Analysis of Braking in Sports

Liguo ZHENG

Taishan Medical University, Taian, Shandong, 271000, China

Keywords: Sports, Braking, Mechanical Effect, Analysis.

Abstract: In games, high-speed movements are required to stop or slow down. It is necessary to focus on applying

body force to braking. In the work, braking to change sports state was conducted with mechanical analysis

to derive the key force of braking—friction force based on Newton laws of motion. After that, mechanical

factors of braking were analyzed according to theorems of momentum and kinetic energy. We obtain the

relation between braking effect and factors including braking force, distance and time. After impact analysis

of braking action and power source, mechanical principles were applied to achieve a better braking effect by

examples.

1 INTRODUCTION

In sports, human body was usually at a high-speed

state. Human body was required to slow down or

stop in games including dash, gymnastics, skiing,

skating, football, basketball, etc. An unsuccessful

braking resulted in failure and accident of sports.

Therefore, mechanical effect analysis played an

important role in completing sports and obtaining

better competition results. Games were conducted

with mechanical effect analysis based on physical

principle of nature.

2 MECHANICAL PRINCIPLE

ANALYSIS OF BRAKING IN

SPORTS

2.1 Relation between Body Motion

State and Applied Force

There are two motion states of body including

stationary and uniform motion according to

Newton's first law of motion law of inertia. Body

motion can be described as the result of exogenic

action.

Newton's first law of motion can be expressed as

follows.

0 0

= ⇒ =

∑



where

∑



is the resultant force; v the speed; t

the time.

If there is no external force (Fi = 0), then the

body will be static (v = 0). The Equation Fi = 0 can

be divided into two conditions including bodies with

a friction force of 0 and with no friction force. The

forces are applied to the body to derive phenomenon

of stationary-to-motion and motion-to-stationary.

There are kinds of forces applied to the body, such

as traction, resistance, gravity and support force.

Motion state of the body is affected by resultant. If

certain force is dominant, it will cause the motion

result of the body. E.g., if a car is started and given

enough oil, the traction will be larger than

resistance. The resultant is more than 0, and the car

is in a steady state. If the oil is not enough, the

traction will be equal to resistance. The resultant is

0, and the car keeps moving in a steady state. If the

brake is hit, the traction will be smaller than

resistance. The resultant is less than 0, and the car is

in a decelerated motion. In sports, we focus on

mechanical effects of braking including the body

with a larger traction, zero resultant and decelerated

motion.

2.2 Relation between Applied Force

and Accelerated Speed in a Motion

State

The accelerated speed increases with the increase of

the applied force based on Newton's second law of

240

Zheng L.

Mechanical Effect Analysis of Braking in Sports.

DOI: 10.5220/0006023202400243

In Proceedings of the Information Science and Management Engineering III (ISME 2015), pages 240-243

ISBN: 978-989-758-163-2

motion. For equivalent force, the body with smaller

mass has a larger accelerated speed. The body with a

mass to certain extent has no accelerated speed. The

directions of the force and

∝

where

is the applied force (N); mass (kg);

accelerated speed (

m s

Human is the body with kinds of motion states in

sports. Newton's second motion law illustrates

change of motion state and relation between applied

forces. Therefore, for braking deceleration, the

baking force is the key factor while the mass of body

is determined. If the braking force is larger, the

accelerated speed will be larger. The braking in

high-speed motion will be efficiently achieved.

2.3 Friction Force

—

A Key of

Achieving Braking in Sports

In the process of human body motion, traction is

produced by friction of body muscle. The resistance

of body motion, including wind and friction force,

comes from body muscle motoricity. As the source

of main braking force in sports, the motoricity can

apply friction and resistance to human motion. For

human body at a high speed, larger resistance and

shorter time will cause a larger accelerated speed

and better braking effect.

Mechanical effect of body from motion to static

state is analyzed to derive braking effect in sports.

Accelerated traction and braking resistance are

realized by friction between body and ground. The

friction is in proportion to pressure and friction

coefficient. Therefore, braking force of body motion

is determined by pressure, friction coefficient and

reacting force.

For every action, there is an equal and opposite

reaction based on Newton's third law of motion. An

example shows a person sits in a chair. The pressure

of body and the support force of the chair are a

couple of actions. In sports, the pressure that body

applies to the ground and the support force that

ground applies to the body are a couple of actions.

Then, the friction is produced to achieve traction and

braking force of body motion.

The pressure that body applies to the ground is

constant in high-speed motion. The friction is in

proportion to friction coefficient. The friction

coefficient has a close relation with sports shoes.

Good sports shoes are designed considering

mechanical performance, beauty, bearing and

friction coefficient. Different characteristics of

sports make friction coefficients of designed shoes

different. In general, kinds of patterns and hobnails

on the soles are designed to increase traction and

braking force.

For braking effect of human body in sports, we

focus on analyzing change laws of momentum and

kinetic energy.

3 RELATION BETWEEN

MECHANICAL BRAKING

FACTORS IN SPORTS

3.1 Kinetic Analysis of Braking in

Sports

Energy produced by object motion is called kinetic

energy. Energy production is a process of dong

work. E.g., people get hot and sweat because

thermal energy is produced. In braking process, the

braking force does work to change the object from

motion to static state. The work is half of the product

of mass and the square of speed. While the speed is

the same, the cars with different masses have

different kinetic energies. A truck has a larger

braking distance than a car with the same speed. For

the same car, the kinetic energy at high speed is

larger than that at low speed. Therefore, people are

required to drive slowly for safety. The result of

synthetic action to an object is expressed as follows.

2 2

1 1

2 2

W mv mv

= −

Kinetic principle reflects cumulative effect of

force in space. It can be expressed as follows.

2 2

1 1

2 2

Fs mv mv

= −

The mass of human body is constant in the

movement. Therefore, the change of kinetic energy

is determined by the speed of movement. While

speed and kinetic energy are the same, braking force

is inversely proportional to braking distance, and

proportional to the square of speed. Consequently,

the influence of speed to braking force is larger than

braking distance.

3.2 Momentum Analysis of Braking in

Sports

Motion effect can be reflected by momentum

product of object mass and speed. Momentum effect,

Mechanical Effect Analysis of Braking in Sports

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Mechanical Effect Analysis of Braking in Sports

241

determined by object mass and speed, can be

expressed as Ft=m

∆

v. In time axis, momentum law

is used to express accumulation of force results. So

we obtain that momentum is in proportion to mass

and speed.

Law of conservation of momentum is expressed

as follows.

2 1

Ft mv mv

= −

In sports, human body follows law of

conservation of momentum. As the mass of human

body is definite, the momentum of human body is

determined by the speed. The human motion braking

process is a sharp change of speed. The braking

momentum is in proportional to braking force and

time. While braking force is constant, the change of

braking momentum is proportional to braking time.

When the change of momentum is constant, the

braking force is reversely proportional to braking

time. Therefore, braking effect can be improved by

increasing braking force and time.

4 MECHANICAL ANALYSIS OF

BRAKING ACTION IN SPORTS

In sports, braking action has great influence on

braking force. The addition of pressure contributes

to the form of larger braking force in short time.

E.g., athletes raise commencing height and jump

distance by high-speed approach in long jump. The

athletes realize safe landing by forward stroke of

legs and feet, thus avoiding falling to the ground.

Mechanical analysis of this braking action is

conducted. The forces applied to athletes in a

jumping state are gravity and wind resistance. In

long jump, the athletes form a parabolic curve of

high-speed. The athlete has an inertial force forward

to form momentum and kinetic energy of human

body. Meanwhile, there exists downward gravity

acceleration and kinetic energy. At the moment of

landing, legs and feet produce ground support by

forward stroke. The inertia of athletes makes a huge

friction between legs and ground. The friction force

is proportional to pressure while friction coefficients

and areas are the same. The huge friction force will

result in sudden stop of athletes' legs. If the athlete

does not stop, he will fall down by effect of inertia.

The athlete can increase braking time by forward

stroke and bending of legs to avoid falling. The

control of braking force and time can decrease the

reacting force of ground to achieve effective braking

of forward and downward action.

5 POWER SOURCE AND

INFLUENCE OF BRAKING TO

HUMAN BODY

Braking force comes from internal force of human

body produced by muscle. Tensile force originates

from muscle contraction, and support force from

bone and soft tissue. In sports, braking force should

be supported by bone and soft tissue. Overlarge

braking shock will cause body hurt. E.g., in high

jump, the body should fall to the buffer cushion to

raise braking time. Otherwise, the huge braking

counterforce will hurt human body.

6 CASE ANALYSIS USING

MECHANICAL PRINCIPLES IN

SPORTS

In sports, braking force is added to achieve prompt

braking in a short distance. E.g., some students go

climbing. A girl trips down the hill. Suddenly, a boy

calls her to stop because there is a cliff ahead. The

smart girl slows down with her hip on the ground. At

last, she is lucky to stop. Now we analyze braking

mechanical effect of the girl. The forces applied to

the girl are gravity, ground supporting force, forward

traction and braking friction. The angle between

gravity and ground supporting force is less than 180

degree in the slope. The combined action of the two

forces produces a propulsive force downward along

the slope. The traction derived from gravity is added

with the propulsive force to produce accelerated

speed. The accelerated speed makes it difficult to

stop in a finite distance. The girl applies resistance

by feet while stopping traction. The friction

resistance applied by her muscle is partially offset

by propulsive force downward. The small friction

resistance cannot achieve complete braking within

finite distance. Then she sits on her hip to increase

the friction force between body and ground. The

friction force is proportional to the area while

friction coefficients and pressures are the same.

Therefore, the friction force is larger than propulsive

force downward, thus achieving braking in finite

distance. Finally, she stops before falling down the

cliff.

7 CONCLUSIONS

Consequently, the braking effect in sports can be

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ISME 2015 - International Conference on Information System and Management Engineering

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improved by addition of braking force, time and

distance based on scientific theories. In daily

exercises, braking effect can be improved by raising

physical quality, muscular contractility and shock

resistance. Besides, we can apply other methods

including increasing friction coefficient of sports

shoes and buffered devices. Multiple braking

methods should be trained to avoid impact damage

of promote braking to human body.

REFERENCES

Cui Li, 1989(3): 47-49. Mechanical effect of braking in

sports, Journal of Teaching and Management (Middle

School Edition).

Meng Xianjuan, 2008(3): 107-109. Pre-squatting brake—

key movement of jerking technique, Journal of Harbin

Institute of Physical Education.

Zhang Zhonghai, 2009(32): 276-281. Basic braking

technique in rollerblade club teaching, Information

Technology.

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Mechanical Effect Analysis of Braking in Sports

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