Clean PUll
The clean and jerk begins with the bar at rest on the platform. In this position, the two forces acting upon the more are the force of normal and force of gravity. The net force is zero as there is no acceleration. Once the lifter pulls the bar up, it begins to accelerate. The force applied to the bar (Fig.1c) is greater than the gravitational force to get the bar moving. The net force can then be found as the net force is equal to the force applied (Fig.1a). When lifting the barbell, the partial mass of the lifter is pulling the weight as the centre of mass changes. The segments used are the thighs (0.100M) multiplied by two since the lifter has two thighs and the shank (0.465M) which is the shin (Fig.1a). The mass of the feet are ignored.
Catch
After accelerating the bar up from the ground, the lifter catches the bar on their anterior deltoids in a low front squat. Here the lifter is in the eccentric phase of the lift.
In the low squat, the lifter is at rest where the gravitational force is the total downward force acting upon them. The force of gravity is the force of attraction between two objects due to their mass. Here I found the force of gravity on the lifter and on the bar to find the total downward force. This is shown to the left (Fig.2).
The lifter must then exert a force greater than 823.2N to lift the weight up to the concentric phase (standing position). In order to find the amount of force the lifter produced, I solved for the net force, the sum of all forces on an object, as the net force is equal to the ground reaction force (Fig.4). I solved for the ground reaction force by subtracting the gravitational force from the net force (Fig.5). The mass is found using the anthropometric table which gives the segment mass as a fraction of the body mass and the centre of mass as a fraction of their lengths. I use the anthropometric table as the centre of mass has changed and the lifter is only using its partial mass to lift the weight. I used the H.A.T. segment (greater trochanter/mid rib) as this is the segment of bodyweight that the lower body will be lifting. 67.8% body weight lifting up the weight of bar as 40.002kg is the partial mass lifting the bar as shown below (Fig.3).
The lifter must then exert a force greater than 823.2N to lift the weight up to the concentric phase (standing position). In order to find the amount of force the lifter produced, I solved for the net force, the sum of all forces on an object, as the net force is equal to the ground reaction force (Fig.4). I solved for the ground reaction force by subtracting the gravitational force from the net force (Fig.5). The mass is found using the anthropometric table which gives the segment mass as a fraction of the body mass and the centre of mass as a fraction of their lengths. I use the anthropometric table as the centre of mass has changed and the lifter is only using its partial mass to lift the weight. I used the H.A.T. segment (greater trochanter/mid rib) as this is the segment of bodyweight that the lower body will be lifting. 67.8% body weight lifting up the weight of bar as 40.002kg is the partial mass lifting the bar as shown below (Fig.3).
The free-body diagram for this action shows that the ground reaction force (GRF) acts up on the lifter and the force of gravity acts up on the lifter (Fig.6).
Jerk
When the bar is resting on the lifters shoulders, the next step is to push jerk the barbell overhead while landing in a split lunge. The gravitational force exerted at this point is 823.2N(DN) as this is the total downward force (as shown in Fig.2). In order to lift the bar overhead, the lifter must exert a force greater than 823.2N. The force acting on the lifter in the bar drive is the bar reaction force as when the lifter applies a force to the bar, the bar applies the force back onto the lifter (see Newton's Third law).
A partial mass of the lifter is used once again to lift the bar up as the centre of mass has changed. Because the majority of the force and power to drive the bar up comes from the lower body, I used the H.A.T. segment to find the partial mass used. I added the partial mass to the mass of the barbell (25kg) to find the total mass that is being use through the acceleration (Fig.3) in order to find the net force. Once I calculated for the net force, I was then able to find the ground reaction force (GRF) to draw the free body diagram.
A partial mass of the lifter is used once again to lift the bar up as the centre of mass has changed. Because the majority of the force and power to drive the bar up comes from the lower body, I used the H.A.T. segment to find the partial mass used. I added the partial mass to the mass of the barbell (25kg) to find the total mass that is being use through the acceleration (Fig.3) in order to find the net force. Once I calculated for the net force, I was then able to find the ground reaction force (GRF) to draw the free body diagram.
Friction
Friction acts opposite to a motion or the attempted motion. Friction is always parallel to the surface. In the clean and jerk, friction is minimal as there is a vertical acceleration (Fig.8). If the acceleration were at angle, due to improper form, then friction would be a horizontal component and would be equal to the ground reaction force.
Newton's First Law
Newton's First Law of motion states that an object at rest or in motion will stay at rest or in motion unless acted upon by an unbalanced force. In a clean and jerk, the force exerted onto the barbell makes it move. The bar starts at rest on the ground where the net force is zero as the force of normal and force of gravity cancel each other out. The bar will stay at rest unless acted upon by an unbalanced force. A force applied to the bar will allow it to move from its state of rest to an acceleration. Inertia is an objects resistance to change which is affected by mass. Therefore, if the mass of the barbell is greater, it would have a greater inertia also meaning that the lifter would have to produce a greater force in order to lift the bar off the ground. Once the bar is off the ground, it does not travel at constant velocity but accelerates as the net force is greater than zero.
Similarly, in the jerk phase, the bar is at rest on the lifters anterior deltoids and will not move unless acted upon by an applied force. This force generated by the lifter allows the bar to move up overhead.
Similarly, in the jerk phase, the bar is at rest on the lifters anterior deltoids and will not move unless acted upon by an applied force. This force generated by the lifter allows the bar to move up overhead.
Newton's Second Law
In Newton's Second law, the magnitude of the acceleration is directly proportional to the magnitude of the net force and inversely proportional to the objects mass.
FNet=ma
This is notable when finding the net force in the catch. When catching the bar in a squat position, if the upward push on the ground is equal to the force of gravity, there will be no acceleration as the net force equals zero. If the force on the ground is greater than the force of gravity, the net force will be positive resulting in a positive acceleration to bring the bar up (Fig.9). Finally, if the force on the ground is less than the force of gravity, then they will be a negative acceleration, which is the opposite of what needs to happen.
The same results occur in the clean pull and the jerk where the force onto the bar and into the ground must be greater than the force of gravity to bring the bar up. The greater force into the bar and into the ground result in a greater bar reaction force and ground reaction force. Therefore, there is a greater acceleration. A greater acceleration means there is a greater net force as they are directly proportional.
If the you doubled the weight on the barbell, the net force will be half of the original net force as the net force and mass are inversely proportional.
FNet=ma
This is notable when finding the net force in the catch. When catching the bar in a squat position, if the upward push on the ground is equal to the force of gravity, there will be no acceleration as the net force equals zero. If the force on the ground is greater than the force of gravity, the net force will be positive resulting in a positive acceleration to bring the bar up (Fig.9). Finally, if the force on the ground is less than the force of gravity, then they will be a negative acceleration, which is the opposite of what needs to happen.
The same results occur in the clean pull and the jerk where the force onto the bar and into the ground must be greater than the force of gravity to bring the bar up. The greater force into the bar and into the ground result in a greater bar reaction force and ground reaction force. Therefore, there is a greater acceleration. A greater acceleration means there is a greater net force as they are directly proportional.
If the you doubled the weight on the barbell, the net force will be half of the original net force as the net force and mass are inversely proportional.
newton's third law
Newton's Third law states that for every action, there is an equal and opposite reaction. This law is noticeable through the clean and jerk. Firstly, when catching the bar in a squat position, the lifter pushes against the ground which pushes back against their body with an equal and opposite force (Fig.10) allowing the lifter to get back into a standing position. This ground reaction force (GRF) is in the control of the lifter by their coordinated muscle actions (Luhatanen, Komi, 1978). In addition, because the jerk uses primarily the lower body to exert power to bring the bar overhead, the ground reaction force is also acting upon the lift as it is the reaction to the lifters push into the ground. Also, when pushing the bar up overhead, the bar pushes a force back on to the lifter. When the lifter applies a force to the bar, a bar reaction force is applied down onto the lifter in a reaction equal in magnitude and opposite in direction of the action.
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References
Luhaten, P., Komi, P.V. (1978). Kin 335-Biomechanics. Retrieved from http://www.asu.edu/courses/kin335/documents/Linear%20Kinetics%20Lab.pdf
Luhaten, P., Komi, P.V. (1978). Kin 335-Biomechanics. Retrieved from http://www.asu.edu/courses/kin335/documents/Linear%20Kinetics%20Lab.pdf