Pole vault
This activity allows students to analyze the complex kinematics of a pole vault and the associated energy transfers. It develops the ability to break down a sporting movement into distinct phases and to understand biomechanical principles.
The pole vault is arguably the most physically complex event in athletics, combining sprinting, gymnastics, and energy physics in a single explosive movement lasting just 2-3 seconds. The vaulter converts the kinetic energy of a full-speed sprint into elastic potential energy stored in a bending fiberglass pole, which then converts into gravitational potential energy as the athlete is launched over a bar set more than 6 meters above the ground. This chain of energy transformations, from kinetic to elastic to gravitational, provides a spectacular demonstration of the conservation of energy principle. Modern fiberglass poles can store enormous amounts of elastic energy (over 2000 joules), returning it efficiently as the pole straightens, acting like a giant spring. Using FizziQ's kinematic analysis module, students can track the vaulter's motion through each phase of the jump, calculate the energies involved, and verify that the height cleared is consistent with the approach speed and the principle of energy conservation.
Learning objectives:
The student uses the FizziQ kinematic analysis module to study in detail the successive phases of a pole vault. By pointing out the positions of the athlete throughout the movement and calculating the corresponding speeds and energies, the student identifies the key moments of the jump (stop turning release) and analyzes the energy transformations between the athlete and the pole.
Level:
High school
FizziQ
Author:
Duration (minutes) :
40
What students will do :
- Analyze the successive phases of a pole vault using video-based kinematic tracking
- Identify the key moments: plant, pole bend, pole straighten, release, and bar clearance
- Calculate the kinetic, elastic potential, and gravitational potential energy at key phases
- Verify the approximate conservation of mechanical energy throughout the vault
- Understand the role of the flexible pole as an energy storage and transfer device
Scientific concepts:
- Energy transfers
- Sports cinematics
- Elasticity
- Elastic potential energy
- Biomechanics
Sensors:
- Camera (video recording for kinematic analysis)
- FizziQ Kinematics module (frame-by-frame position tracking)
What is required:
- Smartphone or tablet with the FizziQ application
- 'Pole vault' video available in the FizziQ library
- FizziQ experience notebook
Experimental procedure:
Open FizziQ and navigate to the Kinematics module. Load the 'Pole vault' video from the FizziQ resource library.
Set the scale using a known reference in the video (the bar height, which is usually displayed, or the athlete's height).
Define the origin of the coordinate system at ground level, at the position of the planting box.
Track the center of gravity of the athlete frame by frame through the entire vault sequence.
Identify and mark the five key phases: run-up, pole plant, pole bend (maximum), pole straighten, and flight over the bar.
From the run-up phase tracking, calculate the approach speed (v₀) of the athlete just before planting the pole.
Calculate the kinetic energy at the end of the run-up: Ec = ½mv², using an estimated mass of 75-80 kg for the athlete.
At the highest point of the jump (bar clearance), measure the height h of the center of gravity above its initial position.
Calculate the gravitational potential energy gained: Ep = mgh.
Compare Ec and Ep. The potential energy at the top should be approximately equal to the kinetic energy at the bottom, confirming energy conservation.
Note that the vaulter's center of gravity at bar clearance is below the bar (due to the Fosbury-like arch), so the effective height gain is less than the bar height.
Discuss the energy losses (friction, imperfect elastic recovery of the pole, muscular energy added during the vault) and their effect on the energy balance.
Expected results:
A competitive vaulter approaches at about 8-9 m/s, giving a kinetic energy of approximately 2400-3200 J for a 75 kg athlete. The center of gravity rises from about 1.0 m (standing) to about 5.5-6.0 m at bar clearance height of 5.5-6.0 m, giving a potential energy gain of approximately 3300-3700 J. The fact that the potential energy exceeds the kinetic energy by 10-20% reflects the muscular work the athlete adds during the vault (pulling and pushing on the pole). The kinematic tracking will show the characteristic velocity profile: high speed during approach, sharp deceleration at the plant, near-zero horizontal speed during the vertical phase, and moderate speed during bar clearance. Tracking precision is limited by video frame rate and the difficulty of locating the center of gravity during the complex body rotations.
Scientific questions:
- Why is a flexible pole so much more effective than a rigid pole for clearing high bars?
- How does the vaulter add energy to the system beyond the initial kinetic energy?
- Why is the center of gravity at bar clearance lower than the actual bar height?
- What is the theoretical maximum height a vaulter could clear based on approach speed alone?
- How has pole vault technology (pole materials, technique) evolved over the past century?
- What limits the current world record? Is it physics or human physiology?
Scientific explanations:
The pole vault is one of the most complex sports movements, combining running, conversion of kinetic energy into elastic, and gymnastic movement. The kinematic analysis reveals several distinct phases: 1) The run-up: the athlete accumulates horizontal kinetic energy (Ec = ½mv²); 2) The stop: moment when the pole is planted in the stop, initiating the transfer of energy from the athlete to the pole; 3) Bending: the pole bends, converting kinetic energy into elastic potential energy (Epe = ½kx², where k is the elastic constant and x is the deformation); 4) Turning: the athlete pivots from horizontal to vertical position; 5) Relaxation: the pole restores the stored elastic energy; 6) Straightening: the athlete extends his body to maximize height; 7) Letting go: moment when the athlete abandons the pole; 8) The apogee: highest point of the trajectory.
On the horizontal speed graph (Vx), the stop appears as a sudden deceleration, and releasing it as a stabilization of the speed at a low value. On the vertical speed (Vy) graph, the apogee corresponds to the moment when Vy = 0.
The energy balance shows that the final mechanical energy (at the moment of crossing) is generally greater than the initial energy (end of momentum). This “additional energy” comes from the athlete’s muscular work during the jump, particularly when turning and recovering.
Typically, a 70 kg elite jumper running at 9 m/s has an initial kinetic energy of around 2800 J. The pole can store up to 1500-2000 J, and the athlete can add 400-600 J through muscular work.
The technical complexity of this movement explains why this discipline requires years of specific training.
Extension activities:
- Why is a flexible pole so much more effective than a rigid pole for clearing high bars?
- How does the vaulter add energy to the system beyond the initial kinetic energy?
- Why is the center of gravity at bar clearance lower than the actual bar height?
- What is the theoretical maximum height a vaulter could clear based on approach speed alone?
- How has pole vault technology (pole materials, technique) evolved over the past century?
- What limits the current world record? Is it physics or human physiology?
Frequently asked questions:
Q: How do I estimate the center of gravity of the vaulter during complex rotations?
R: During upright phases, the center of gravity is near the navel. During inverted or tucked positions, estimate the geometric center of the body mass. Consistency matters more than absolute accuracy for comparing energies at different phases.
Q: The kinetic energy at the bottom is less than the potential energy at the top. Does this violate energy conservation?
R: No. The athlete adds muscular energy during the vault by pulling and pushing on the pole. Competitive vaulters add approximately 500-1000 J of work during the vault, which supplements the kinetic energy of the run-up.
Q: Why do vaulters use fiberglass poles instead of metal?
R: Fiberglass poles can bend significantly (up to 70-90 cm of deflection) without breaking and return nearly all the stored elastic energy. Metal poles are either too rigid (limiting energy storage) or too brittle (breaking under extreme bend).
Q: Can I use this analysis to predict how high a vaulter could jump?
R: The theoretical maximum height (ignoring muscular contribution) is h = v²/(2g), which gives about 3.3 m above the starting center of gravity for a 9 m/s approach speed. The additional muscular work and technique allow competitive vaulters to exceed this by 1-2 meters.