Acceleration
Introduction:
Acceleration is defined as the rate of change of velocity with respect to time, thus the concepts of velocity also apply to acceleration. In the velocity-time graph, acceleration is reprented by
奥运币the slope of the line, with the steepness and direction of the slope indicating the nature of the acceleration – whether it is positive, negative or zero, and thus indicating the relationship between them. Similar to velocity, acceleration is a vector quantity meaning that it is both magnitude and direction aware. The term acceleration is often ud looly associating it with speed but this is not the ca. An object can be moving at speed yet not be it
has a constant velocity. If the velocity of an object is not changing then no acceleration is occurring. The basic equation for acceleration is:cad入门
Acceleration = ∆ Velocity (ms⎯¹)
Time (s)保持健康英语
The International System of Units (SI) is a list of the various metric systems. SI is built on ven fundamental standards called ba units. All other units are various combinations of the ven bas, attained by the multiplying, dividing or powering of the bas. As the common SI unit for velocity is meters per cond (ms⎯¹) and the SI unit for time is conds (s) then acceleration is usually measured as meters per cond per cond (ms⎯²). However any unit of length divided by any unit of time yields an acceptable unit of km/hr/s.
As mentioned earlier, acceleration is a vector meaning it is direction nsitive. The direction of acceleration is determined by two main factors:
¾Whether the velocity of the object is increasing or decreasing
¾Whether the object is moving in a positive or negative direction
Any change in velocity results in an acceleration. When an acceleration value is positive, this does not necessarily mean that the object is speeding up. A positive acceleration can indicate either that the velocity of the object is increasing in a positive direction or decreasing in a negative direction. Alternatively, if the acceleration is negative, velocity can either be increasing in a negative direction or decreasing in a positive direction.
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The general rule of thumb is that when the velocity of an object is increasing, acceleration is in the same direction as the velocity. However, when the velocity of an object is decreasing then acceleration is in the opposite direction to its motion. This is sometimes referred to as deceleration.
Objectives:
¾Define and analy acceleration in sport specific situations using the Quintic software
¾To compare the accelerations in various sports situations
Methods:
¾The videos have been digitid and calibrated using the Quintic software.
¾Data has been exported to an excel file where it was ud to calculate linear acceleration, horizontal acceleration and vertical acceleration. Graphs have been prepared using this information.
¾Still images have been captured from videos to outline different stages of the exerci
Functions of the Quintic Biomechanics and
Coaching Software ud:
•1 Point Digitisation Module
•Calibration
•Interactive Graph and Data displays
•Export Data
•Multi-Image Capture中国杰出女性
Results:
All the different accelerations (linear, horizontal and vertical) from the four activities – bench press, race walking, golf putt and swimming, were analyd using single point digitisation. Every frame of the video from the start of the movement to the end was digitid.
Linear Acceleration
-45
-35
-25
-15
-551525
35
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45
江西专科分数线0.51 1.5Time (s)A c c e l e r a t i o
n (m s ⎯²)Bench Press Golf Club Swimmer Race Walking
Graph 1: Linear Acceleration Graph 1 shows the linear acceleration of the four sports. Race walking has the highest and most variable linear acceleration ranging from -40.07ms ⎯² to 42.35 ms ⎯². The rest of the sports all experience significantly lower linear acceleration values, with swimming reaching a maximum acceleration of 5.71ms ⎯² and the other two sports reach minimal accelerations of 1.42ms ⎯² and 0.88ms ⎯² for the bench press and golf club respectively.
As stated in the introduction, acceleration is a vector and has both magnitude and direction. All horizontal and vertical acceleration graphs show the component acceleration in the respective directions. However, the linear acceleration graphs only show the magnitude of the
acceleration. The direction of any linear acceleration is given by the resultant sum of horizontal and vertical accelerations.
Graph 2: Acceleration of the Golf Club
Graph 2 and figure 1 (below) illustrates acceleration of the golf club. This graph has been divided into three different phas of the golf swing during the putt shot. Pha 1 is the back swing of the club, pha 2 is the return of the club to the starting position and pha 3 is the follow through of the club after contact with the ball.
Figure 1: Acceleration of a Golf Club
During pha 1, the initial movement of the club caus a positive linear acceleration. Midway through this pha, the velocity curve changes direction as the club is preparing to slow down approaching the top of the backswing. When the curve changes direction, acceleration is zero. Linear velocity now begins to decrea resulting in deceleration. At the end of pha 1, the club is temporarily static as it changes direction hence no acceleration is occurring. Pha 2 begins from the top of the back swing. The club begins to move in a positive direction towards the ball thus linear acceleration increas positively but as the velocity becomes clor to a constant value, the rate of acceleration slowly begins to decrea. Just before impact, acceleration changes rapidly from 3.38ms⎯² to -13.28ms ⎯², due to a decrea in linear velocity. During pha 3, the club has just hit the ball. There is an initial acceleration during the frame after contact, but then deceleration as the velocity of the club decrea during the follow through. Horizontal acceleration of the club varies due to the direction in which the club is moving. During pha 1, the initial horizontal acceleration of the club is -2.37ms⎯². As the club is moving in a negative direction, acceleration is negative. However, as the velocity begins to decrea, the acceleration returns to zero and starts to increa positively. Pha 2 es the acceleration increasing initially but as the horizontal velocity becomes constant, acceleration decreas returning to zero. As the ball is hit, horizontal velocity of the club decreas resulting in deceleration.
There is little variation in the vertical acceleration of the golf club. During the back swing, vertical velocity increas becoming constant meaning that vertical acceleration, which is initially 0.86ms⎯² returns to zero. As the vertical velocity is on the ri again, vertical acceleration also increas to a value of 0.84ms⎯². By the end of the first pha, vertical velocity has decread causing the vertical acceleration to increa negatively to -1.27ms⎯².
Acceleration of the race walker is constantly changing with each step, a step being defined as heel of contact of right foot to subquent heel contact of left foot. When digitizing the video, the hip was ud as the single point of digitisation. Due to acceleration being direction nsitive, substantial amount of the variation can be accounted for by the continuous change in the hip on, causing an acceleration.
a positi
Graph 3: Acceleration of a Race Walker
红掌水培养殖方法However, a pattern can be en in the acceleration for every step. Linear velocity decreas immediately at heel contact and continues to decrea during the first portion of the suppor period. As the walker extends his other leg in the latter portion of the support period, the velocity increas. Thus, the corresponding acceleration-time graph of a walker during the support pha shows distinct negative and positive accelerations. It can be en that the walke has higher acceleration values during the cond pha of the support period meaning that the walker slows down in the first portion of th t r e support and speeds up in the latter portion. To aintain a constant average velocity, the walker must gain as much speed in the latter portion of the pha as was lost in the first pha.
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Figure 2: Race Walking Acceleration Figure 2 demonstrates the changing hip heights of the walker during one step. The green line shows the initial hip height while the red line shows the hip movement during the video. As ca be en from the pictures, as the walker is stepping with his right foot, hip right hip ris above the initial height. Going into the first part of the support ph n a, and again in the cond part, the hip lowers slightly. By the time the left heel makes contact with the ground, the right hip is nearly back to its initial height while the left hip is rising.
