Course:KIN355/2020 Projects/Inertia
Defining the Concept and Its Importance
Inertia can be defined as the resistance force of any object to change in the state of motion (Verlinde, 2011). In this context, we can look at Newton’s first law of motion which states that an object at rest or motion will continue to be in the same state unless acted upon by another force (Olzmann, 2014). Some of the physical forces creating inertia (change in the constant state of motion) on the surface of the earth are gravity, friction, and air resistance. In the realm of child movement development, we will examine the effects of these forces and how they alter physical movement and create adaptation in children. Gravity is one of the fundamental forces shaping our muscles tone and strengths since the day we were born. All major developmental milestones related to children's movement are essentially different versions and phases of working against gravity (Jansen et al., 2014). Baby crawling is one example of the work of gravity where the right and left arms and legs push and pull against this force in different angles, magnitudes, and coordination (Jansen et al., 2014). If it wasn’t for gravity we would have much less muscle mass and very weak muscles to carry the everyday tasks. This is one of the reasons why astronauts return to earth with weaker muscles after a long journey in space (Kohrt, et al., 2009). Gravity is responsible for the development of posture muscles and bone density which in turn facilitate movement (Kohrt, et al., 2009). Ultimately, learning to move is learning to work with or against gravity. Friction is the resistance force that always opposes the motion of one surface against another surface (Walker, 2003). In our topic’s context, we can look at friction as the force between foot heel and hand palm that creates the resistance force between the two surfaces to move back and forth. Friction plays an important role in developing synchronous strides when the child first starts learning to walk (Shacham et al., 2010). Air resistance is at large a small force acting on the movement of the child. It is mostly experienced to a greater degree when the limbs are at movement not the core of the body. Overcoming gravity, friction and air resistance are some of the basic challenges a new born face to overcome the inertia of movement. Furthermore, inertia can be examined in linear and angular dimensions of movement. Linear and angular movements are some of the rudimentary forms of motion developed by children soon after birth and during the development of the central nervous system (Yoganandan et al., 2009). Angular movement for the most part is an important motor development in children since it is practiced in many physical activity settings like the playground or with the toys that children play with. Kicking a ball on the playground is an example of gross motor skill and rotating hands while moving a toy car on the ground is a fine motor skill involving angular movement and the concept of inertia.
Role in Childhood Development and Contemporary Considerations
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In the context of child movement development and inertia, we will be looking at 2 different sports that children engage in large numbers along with the role of the moment of inertia and how angular movement by the limbs are developed and master’s in children in these sports. Moment of inertia also known as rotational inertia, angular mass or the mass moment of inertia of a solid body is the value expressing the body’s resistance to angular motion (Lebiedowska & Polisiakiewicz, 1997). It is the toque required for a specific angular acceleration about a rotational axis (Lebiedowska & Polisiakiewicz, 1997). Calculating the body’s moment of inertia is a complex process. However, it depends largely on the mass of the object and the distance between the axis of rotation (Uchida et al., 2019). These calculations are often used by biomechanical studies and athletes trying to reduce their moment of inertia during sporting competitions by constantly trying different body configurations of exercise. Diving athletes are famous for trying different diving positions in a bid to reduce their movement’s moment of inertia. In physiology, it is usually calculated by multiplying the mass of the body with the square of the height (Uchida et al., 2019). Correct execution of many sophisticated movements in various sports like gymnastics or figure skating is dependent on the moment of inertia. The larger the value of the moment of inertia in a movement, the more difficult it is the execution of that movement (Lebiedowska & Polisiakiewicz, 1997). There have been a number of studies conducted to better understand the dynamics of physical activity and age and body type relationship with the moment of inertia in children. Physical growth in children changes their inertial characteristics (Jensen, 1981). Moreover, this “change in inertia represents constraints which the body must adapt to if the level of motor performance is to be maintained or improved” (Jensen, 1981). According to Jensen, (1986), the value of the moment of inertia becomes larger with activities involving the mass centroid of children. For example, a backflip in gymnastic has a greater value of the moment of inertia than a limb extension in soccer.
In gymnastics when a child performs a somersault, “the linear and angular momentum along with a particular control of inertia during the flight phase constrain the possibilities for action” (Heinen & Nicolaus, 2016). The human movement mechanism is convoluted and dependent on many factors. However, on this subject, we could argue that there are stable coordination states when carrying out somersaults to some extent (Heinen & Nicolaus, 2016). In an academic study conducted to explore the manifold of movement options and coordination states of gymnastics, Heinen & Nicolaus, (2016) concludes that the best method to perform a single somersault in conjugation with a larger moment of inertia is to perform a “tucked position, a longer duration to achieve the tucked position, a longer duration of staying tucked, and an intermediate moment of inertia during landing.” In this way, a large amount of movement options is combined with an upright landing and therefore the highest probability of success when achieving an individual somersault (Heinen & Nicolaus, 2016). Jensen, (1986) longitudinal design study of 12 subjects also examines the link between age and inertia, stating that as the child grows older, the moment of inertia also increases. In addition, puberty and sex are other factors factor that creates significant changes to rotational movement and the adaptation period making it more difficult and extensive (Jensen, 1986). All the male participants of this study produced a smaller value of the moment of inertia when performing the same exercises as their female counterparts of the same age. Furthermore, the moment of inertia increases 3.5 times faster in children 10 years of age and older than their younger peers in this study (Jensen, 1986). This suggests that there is more flexibility in children's movement at a younger male age population. This highlights the importance of enrolling children in physical activity classes at a younger age to create better-performing athletes in the future. The development of children’s movement and inertia depends on individual differences; however, physical education, body mass, and height are barometers of improvement and mastery. Lastly, in order to improve the moment of inertia in children, they must engage in activities that have greater angular and linear momentum. For example, figure skating spin is a great illustration of a movement that requires a great angular/vertical impulse that gives greater angular/vertical momentum (Jensen, 1986).
Practical Applications
Activity/Game #1
Title
Swinging with inertia
Purpose statement
The purpose of this activity is to provide children with the ability to develop their movement behaviours through the concepts of Newton's first law of motion--inertia. The first law implies that an object at rest or motion will continue to be in the same state unless acted upon by another force (as cited in Olzmass, 2014). The following statement will be expressed towards the purpose of this activity. Children that are in the first group are at rest, while the second group resembles the force that is being applied to the constant variable. In other words, while the first group of children are in their resting position, the moment the second group begins to swing the first group of children back and forth, they are no longer in their same rested state because they have been acted upon by another force; thus, being the second group. This activity provides children with the incorporation of both their upper and lower body segments, where the upper body segments can resemble the need to push the partner, in order for them to move back and forth; which is facilitated with the strength of the arms. Furthermore, when children are swinging, they are using the core muscles and arm strength to maintain their balance while holding onto the swing chains. The lower body segments can resemble the need to maintain the momentum of swinging back and forth with the legs while on the swing, and the need to run towards the teacher in order to complete the task.
Target age
The specific target age for this activity is 9 year olds. The reasoning behind this specific age group is that these children are able to understand the concepts of the activity, both mentally and physically. Assuming the proper instructions are given by the teacher, this activity is simple and easy for this age group to follow. This age group has most likely been exposed to a similar activity during recess or lunch time at their elementary schools, meaning this activity will further enhance their motor development.
Equipment needed
The equipment needed for this activity involves providing children with colourful pinnies, which will distinguish between the first and second groups. The swing-set will provide the necessary equipment needed to fulfill this particular task. Similarly, teachers must have signs that have a green and red colour on either side, for children to visually see and engage in “go” and “stop” behaviour.
Environmental space/set-up
As for the environmental set-up of this activity, it involves the first group of children being positioned in front of the swings and seated. The second group of children will be standing behind the first group of children in the beginning phase of the activity. The teacher will be positioned facing centered on the opposite side of the children.
Instructions
Before the start of the activity, the teacher is to provide the children with the appropriate instructions and behaviours on how to engage in the activity. Firstly, the teacher must assign the children to their designated groups. The teacher will verbally construct children to face towards the teacher, in a single horizontal line. The teacher will then choose a starting point from which to count from, from either ends of the single horizontal line. The counting will consist of being assigned to either the “first” or “second” group. Furthermore, the purpose of assigning children to two different groups, relies heavily on the concepts of facilitating Newton's first law of motion--inertia. Thus, children within the first group will be in front of the children in the second group and remain constant while seated on the swing. Children within the second group will be behind the children in the first group and remain constant in the beginning. The teacher will be in front of the children, although facing towards them in a centered approach.
Secondly, now that the children have been positioned into their designated spots, it is time to explain the roles of the teacher and two-groups. The teacher will have a green sign that reflects the meaning of “go” and a red sign to represent “stop”. The children in the second group will need to look at these commands throughout the activity in order to respond accordingly. The first group will be seated on the swing, while the second group will stand behind them, with their arms extended towards the first group. When the teacher shows the green sign, the second group will begin to push the first group, until the first group has successfully started to swing back and forth. The first group will swing back and forth on the swing with the momentum of their legs executing this movement, while their arms are holding onto the swings chains for balance. In the meantime, the second group will safely remove themselves away from the first group, taking a few steps back in the opposite direction of the swings. When the teacher presents the red sign, the first group must start to slow down their momentum and stop until they remain constant with the swing.
Thirdly, once the designated objective has been achieved, the children in the first group will now become the second group and the second group will become the first group. This is to ensure that each child receives an equal opportunity of playing between the first and second group. The teacher will know when to facilitate this switch by counting to the number five, which will resemble the amount of times that the first group is allowed to swing before the teacher presents the red sign to signal stop. Lastly, because there are many rules associated with this activity, it is important for the teacher to verbally go through and explain to the children how to act accordingly in their designated roles, prior to the start of the activity. Hence, the children must follow the designated signs for when to start and stop their movement and the children must respect each other and not excessively push their peers to the point that leads to unnecessary conflict or injury.
Modifications
To reduce boredom and repetitive gameplay amongst children, teachers are able to provide alternative modifications to the activity. The activity can turn into a game, where the first and second group are paired up together and have the objective of finishing first. For instance, the first and second group start in their designated positions and follow the same procedures as in the activity. The first group will then swing back and forth only one time and come to a complete stop, in order to let the second group initiate the same procedure. Once the second group engages in their back and forth movement and comes to a complete stop, they must run towards the teacher. Therefore, the first child from the second group to reach the teacher first will be considered the ‘winner’ for that particular round.
Activity/Game #2
Title
Traffic lights with inertia
Purpose statement
The purpose of this game is to provide children with the ability to develop their movement behaviours through the concepts of Newton's first law of motion--inertia. The first law implies that an object at rest or motion will continue to be in the same state unless acted upon by another force (as cited in Olzmass, 2014). The following statement will be expressed towards the purpose of the activities. Children in the first group “inertia”, are constant in their position, while the second group “force” acts as the external force that is moving the “inertia” from their constant position. This activity provides children the opportunity to incorporate both their upper and lower body segments. The upper body segments can resemble the need to push the person in front, in order for them to move forward, incorporating the strength of the arms to facilitate such action. The lower body segments can resemble the need to walk, jog, or run towards the teacher in order to complete the task. Moreover, the legs can be used to maintain balance when trying to stop, once the red sign signals to do so.
Target age
The specific target age for these activities is 9 year olds. The reasoning behind this specific age group is that these children are able to understand the concepts of the activity, both mentally and physically. Assuming the proper instructions are given by the teacher, this activity is simple and easy for this age group to understand and follow.
Equipment needed
The equipment needed for this activity includes three separate signs that are coloured green, yellow, or red, in order for children to visually understand when to go, slow down, or come to a complete stop. The teacher may also provide children with colorful pinnies to wear, in order to distinguish between the first and second group.
Environmental space/set-up
The environmental set-up of this activity involves the first group of children to be positioned at the back end of the gymnasium, where they are equally spaced along the gymnasium in a horizontal line, with at least an arms length between each other. The second group of children are equally spaced behind the children in the first group. The teacher is positioned at the other end of the gymnasium and is centered towards the children. The gymnasium or playing area should be free of any other equipment or barriers, to avoid distractions.
Instructions
As for the instructions, the teacher is to provide the children with the appropriate instructions before starting the activity. Firstly, the teacher must assign the children to their designated groups. The teacher will verbally construct children to face towards the teacher in a single horizontal line and will choose a starting point from which to count from. The counting will consist of the verbal assignment to either the “first” or “second” group. Children that are selected as “first” will be referred to as the first group of children or “inertia”. Children selected as “second” will belong and be referred to as the second group of children or the “force”. The teacher will represent a traffic light. Moreover, the purpose of assigning children to two different groups, relies on the concepts of facilitating ‘inertia’. Children within the first group will be in front of the children in the second group and remain constant, while the children within the second group will be behind the children in the first group and remain constant in the beginning. The teacher will stand on the opposite side, facing the children, and remains constant throughout the whole activity.
As for the roles of the teacher and children, the teacher, or “traffic light”, will have a sign that reflects the colour green for “go” and the color red for “stop”; and the “force” group will need to pay attention to these commands throughout the duration of the activity. The “inertia” group will have the role of standing still in one spot. Likewise, the “force” group will initiate the role of standing still in one spot directly behind the “inertia” group; however, their arms will be held in front of them and pointed towards the “inertia” group’s back. When the “traffic light” turns green, the “force” group will attempt to push the “inertia” group in front of them, as long as the “traffic light” does not turn red. Once the red sign is signaled, the “force” group will need to control the “inertia” group and stabilize their position, so that they surrender in one spot. The children in the beginning phase of the activity are too walk, while being pushed or pushing others (see the modifications section for other alternatives). These commands are to be facilitated by the “traffic light”, until one of the “force” groups has successfully pushed their “inertia” partner past the “traffic light”; in this case, the teacher. The “traffic light” or teacher will serve as the end point throughout the activity, which will allow children to visually represent their objective.
Thirdly, once the winning “inertia” and “force” group has successfully passed the “traffic light”, the teacher will ensure children get an equal opportunity of playing both roles. The teacher is able to provide this by switching the groups each time a successful group wins. In terms of groups, the children that are labelled as “inertia” will become the “force” and appropriately switch roles when instructed to by the teacher.
Finally, it is important for the rules associated with this activity to be verbally explained to the children prior to the start of the activity. Firstly, the “force” partner must be pushed by the “inertia” partner, in order to move themselves towards the “traffic light”. In the event that cheating is to take place, the partners will both have to go back to the starting point. Secondly, if children move when the “traffic light” signals red, they also have to go back to the starting point. Thirdly, children must respect each other and not excessively push their peers, in order to avoid any conflict or injury.
Modifications
To reduce boredom and repetitive gameplay amongst children, teachers are able to provide alternative modifications to the game of traffic light. These modifications include adding another command for the “traffic light”; more precisely the color of yellow representing the motion of ‘slow down”. This new command will indicate that children are to continue to walk, however, must do so very slowly. This new command will increase the physical activity that children are engaged in, while further developing the children's concepts of inertia and movement behaviours. Another concept of modification includes altering whether the children can walk or run during the “go” signal. For instance, if the “traffic light” turns “green”, then the children are able to run; however, if the “traffic light” turns “yellow”, children must walk slowly. Ultimately, these modifications are best facilitated when the children have understood the concepts of the game and have participated in it numerous times.
Summary
- Inertia can be described using Newton’s first law of motion, which states that an object at rest or motion will continue to be in the same state unless acted upon by another force.
- Children begin to face the challenge of overcoming inertia from the day that they are born, and as they grow older.
- The three main physical forces that create inertia (change in the constant state of motion) on the surface of the earth are gravity, friction, and air resistance.
- Physical education, body mass, and height are barometers of improvement and mastery to overcome inertia in sports and activities.
References
Heinen, T., & Nicolaus, M. (2016). Option selection in whole-body rotation movements in gymnastics. Revista Brasileira De Educação Física E Esporte, 30(1), 29-39. doi:10.1590/1807-55092016000100029
Jansen, K., Groote, F. D., Duysens, J., & Jonkers, I. (2014). How gravity and muscle action control mediolateral center of mass excursion during slow walking: A simulation study. Gait & Posture, 39(1), 91-97. doi:10.1016/j.gaitpost.2013.06.004
Jensen, R. (1981). The effect of a 12-month growth period on the body moments of inertia of children. Medicine & Science in Sports & Exercise, 13(4), 238-242. Retrieved from http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=reference&D=ovfta&NEWS=N&AN=00005768-198104000-00006.
Jensen, R. K. (1986). The growth of children??s moment of inertia. Medicine & Science in Sports & Exercise, 18(4). doi:10.1249/00005768-198608000-00014
Kohrt, W. M., Barry, D. W., & Schwartz, R. S. (2009). Muscle Forces or Gravity. Medicine & Science in Sports & Exercise, 41(11), 2050-2055. doi:10.1249/mss.0b013e3181a8c717
Lebiedowska, M. K., & Polisiakiewicz, A. (1997). Changes in the lower leg moment of inertia due to child's growth. Journal of Biomechanics, 30(7), 723-728. doi:10.1016/s0021-9290(97)00018-3
Olzmann, M. (2014). Sir Isaac Newton's First Law of Motion. New England Review (1990-), 35(3), 99-99. Retrieved October 22, 2020, from http://www.jstor.org/stable/24243076
Shacham, S., Castel, D., and Gefen, A. ( 2010). "Measurements of the Static Friction Coefficient Between Bone and Muscle Tissues." ASME. J Biomech Eng. August 2010; 132(8): 084502. https://doi-org.ezproxy.library.ubc.ca/10.1115/1.4001893
Uchida, H., Uematsu, H., Kawai, Y., Nagao, A., & Sakuma, I. (2019). Study of the Moment of Inertia Ratio of Feed Axes of Machining Centers to Servo Motors (2nd). Journal of the Japan Society for Precision Engineering, 85(6), 577-584. doi:10.2493/jjspe.85.577
Verlinde, E. (2011). On the origin of gravity and the laws of Newton. Journal of High Energy Physics, 2011(4). doi:10.1007/jhep04(2011)029
Walker, S. (2003). Fog, Friction and Force Caps. doi:10.21236/ada420056
Yoganandan, N., Pintar, F. A., Zhang, J., & Baisden, J. L. (2009). Physical properties of the human head: Mass, center of gravity and moment of inertia. Journal of Biomechanics, 42(9), 1177-1192. doi:10.1016/j.jbiomech.2009.03.029