work
In weightlifting, you do work by moving the weights from the ground to the shoulders through a clean or overhead by pushing the bar up. To lift the weights, the lifter must apply an upward force that displaces the weights in the direction of the force. This called mechanical work. (Physics 11, 226)
Clean pull
In the clean pull, the lifter applied a force on the barbell in a upward direction and simultaneously, the Earth applied a force of gravity in the opposite direction (down). In this case, the total work done is on the barbell is the sum of the work done by all of the forces acting on the barbell.
Given: Fg= 823.2N Fa=870N Δd= 1.2m
Required: Wa (mechanical work done by the force applied on the bar)
Wg (mechanical work done by the force of gravity)
Wnet (net force of done by the applied force and force of gravity on the bar)
Clean pull
In the clean pull, the lifter applied a force on the barbell in a upward direction and simultaneously, the Earth applied a force of gravity in the opposite direction (down). In this case, the total work done is on the barbell is the sum of the work done by all of the forces acting on the barbell.
Given: Fg= 823.2N Fa=870N Δd= 1.2m
Required: Wa (mechanical work done by the force applied on the bar)
Wg (mechanical work done by the force of gravity)
Wnet (net force of done by the applied force and force of gravity on the bar)
Therefore, the net work done by the applied force and force of gravity on the barbell is 6.4x10^2 Joules.
Clean
In the clean, the ground reaction force is applied to the lifter to move the barbell in the upward direction from a squat. This force displaces the barbell in that direction.
Given: Fg= 823.2N GRF=1195.7N Δd= 0.4m
Required: WGCF (mechanical work done by the ground reaction force)
Wg (mechanical work done by the force of gravity)
Wnet (net force of done by the ground reaction force and force of gravity to lift the bar)
Clean
In the clean, the ground reaction force is applied to the lifter to move the barbell in the upward direction from a squat. This force displaces the barbell in that direction.
Given: Fg= 823.2N GRF=1195.7N Δd= 0.4m
Required: WGCF (mechanical work done by the ground reaction force)
Wg (mechanical work done by the force of gravity)
Wnet (net force of done by the ground reaction force and force of gravity to lift the bar)
Jerk
In the jerk, the ground reaction force pushes the barbell in the upward direction and the force of gravity pushes it downward. Below is how I calculated work.
Given: Fg= 823.2N GRF=1267.5N Δd= 0.67m
Required: WGCF (mechanical work done by the ground reaction force)
Wg (mechanical work done by the force of gravity)
Wnet (net force of done by the ground reaction force and force of gravity to lift the bar)
In the jerk, the ground reaction force pushes the barbell in the upward direction and the force of gravity pushes it downward. Below is how I calculated work.
Given: Fg= 823.2N GRF=1267.5N Δd= 0.67m
Required: WGCF (mechanical work done by the ground reaction force)
Wg (mechanical work done by the force of gravity)
Wnet (net force of done by the ground reaction force and force of gravity to lift the bar)
Power
Power is the rate at which energy is transformed or the rate at which work is done. Power is a scalar quantity as there is no direction and the unit for power is called watts (W), (Physics 11, 250). Power is calculated using the equation below:
Clean Pull
I can find power for the clean pull as I know the work used and the time it took in order to perform work
Given: Wnet=2.0x10^3J Δt=0.57s
Required: P
I can find power for the clean pull as I know the work used and the time it took in order to perform work
Given: Wnet=2.0x10^3J Δt=0.57s
Required: P
Clean
I can solve for the power generated in the clean as I know the work and the time taken to perform work.
Given: Wnet=8.1x10^2J Δt=0.85s
Required: P
I can solve for the power generated in the clean as I know the work and the time taken to perform work.
Given: Wnet=8.1x10^2J Δt=0.85s
Required: P
Jerk
I found the power the lifter produced in the jerk by using the work and the time it took for the lifter to complete this movement.
Given: Wnet=1.4x10^3J Δt=0.96s
Required P:
I found the power the lifter produced in the jerk by using the work and the time it took for the lifter to complete this movement.
Given: Wnet=1.4x10^3J Δt=0.96s
Required P:
efficiency
Efficiency is the ratio of the amount of useful energy (energy output) to the the amount of energy used (energy input). Efficiency is expressed as a percentage
Clean Pull
I found the efficiency of the clean pull where gravitational potential energy was the energy output and work was the energy input.
Given: Ein=2.0x10^3 J
Clean Pull
I found the efficiency of the clean pull where gravitational potential energy was the energy output and work was the energy input.
Given: Ein=2.0x10^3 J
Clean
Like the efficiency of the clean pull, the output energy is the gravitational potential energy and the input energy is work in the clean.
Given: Ein=8.1x10^2J
Like the efficiency of the clean pull, the output energy is the gravitational potential energy and the input energy is work in the clean.
Given: Ein=8.1x10^2J
Jerk
The efficiency in the jerk is determine by dividing the energy out (Ep) and the energy in (W).
Given: Ein=1.4x10^3J
The efficiency in the jerk is determine by dividing the energy out (Ep) and the energy in (W).
Given: Ein=1.4x10^3J
Conclusion
It appears that this lift is inefficient but this energy transforming process provides all the energy the lifter uses to perform work. The lifter uses chemical energy which is transferred to kinetic energy one the lifter begins to move. The major waste output energy is thermal energy (Physics 11, 244).
It appears that this lift is inefficient but this energy transforming process provides all the energy the lifter uses to perform work. The lifter uses chemical energy which is transferred to kinetic energy one the lifter begins to move. The major waste output energy is thermal energy (Physics 11, 244).
Energy Conservation
The law of conservation of energy states that energy is neither created or destroyed but can be changed into unusable forms of energy (Physics 11, 237). Let's look at the energy transformation diagram of the clean and jerk:
This energy transformation diagram shoe the change of one type of energy to another. We can see that kinetic energy has been transferred into thermal energy. The lifter and the bar have the lowest gravitational potential energy at the beginning of the lift as they start from the lowest height. Height affects gravitational potential as the energy is stored in an object as a result of its vertical displacement. The higher you are, the greater force of gravity applied to you.
Energy Conservation in Clean Pull:
At the maximum height of the pull, there is 1.4x10^3 joules of mechanical energy, if energy was conserved.
Energy Conservation in Clean Pull:
At the maximum height of the pull, there is 1.4x10^3 joules of mechanical energy, if energy was conserved.
Thermal Energy
Thermal energy is the total quantity of kinetic and potential energy possessed by atoms or molecules of a substance (Physics 11, 236). It is often mistakingly called heat energy. Thermal energy in the clean and jerk is wasted energy and causes low efficiency in the movement as kinetic or potential energy was lost to thermal. This type of energy is formed when the body heats up. This energy does not do external work or help you lift weight. Therefore, we know it is wasted energy. We can reduce thermal energy by becoming more efficient by looking at oxygen costs at a given amount of work (Leyland, 2011). Looking at our body's energy systems, the phosphagen system is used primarily in olympic weightlifting as the movement produces maximum bouts of powerful and explosive exercise. However, when the phosphagen system runs low on fuel, the glycolysis and oxidative systems kick in. Therefore, the glycolysis and oxidative system have to improve to reduce the impact of thermal energy.
Thermal energy can be found using this equation below where m is your total mass, c is the total heat capacity of a human and delta t is your change in temperature.
Thermal energy can be found using this equation below where m is your total mass, c is the total heat capacity of a human and delta t is your change in temperature.
References
DiGiueseppe, M., Howes, C., Speijer, J., Stewart, c., van Bemmel, H., Vucic, R., & Wraight, V. (2011). Retrieved from Nelson Physics 11.
DiGiueseppe, M., Howes, C., Speijer, J., Stewart, c., van Bemmel, H., Vucic, R., & Wraight, V. (2011). Retrieved from Nelson Physics 11.