I will start with a fantastic line from Vladimir M. Zatsiorsky, a professor of kinesiology at Penn State University: ‘that a powerful athlete is always strong; however, a strong athlete is not always powerful’. This can be found in his book The Science and Practice of Strength Training, which is highly recommended for anyone seeking to delve further into strength training.

Vladimir M. Zatsiorsky implies that a powerful individual must be strong and capable of producing high forces. However, being able to produce high forces in itself is not a guarantee that a person will be powerful.

Let's delve into some essential physics to differentiate between speed, power, force, velocity, and explosiveness. These terms are often used in sports but do not all mean the same. There is a lot of confusion about explosiveness and explosive strength training.

**Physics 101 **

**Equations **

Weight: W=mg (weight equals mass times gravity)

Mass: M = f/a (mass equals divided by acceleration)

Force: F = ma (force equals mass times acceleration)

Velocity: V = d/t (velocity equals displacement divided by time)

Rate of Change = R = Δy/ Δx (Change in y divided by change in x)

Speed: S = D / T (speed is distance travelled divided by time elapsed)

Power: Force * Distance ÷ Time (Power equals Force times Velocity)

Work: W = fd (work equals force times the distance)

Impulse: I = Fxt (impulse equals force multiplied by time)

Rate of Force Development: RFD = F/t (Force (newtons) / Time (seconds)

Time: T = D / t (time equals distance divided by speed)

**Matter -** anything that takes up space and can be weighed, i.e. it has volume and mass.

**Work **

Work is defined as *the product of an external force acting on an object and the displacement the force has causes*

** Work** is the product of the component of the force in the direction of the displacement and the magnitude of this displacement.

** Work is the energy needed to apply a force to move an object** a particular distance, where force is parallel to the displacement.

Work is the energy needed to apply a force to move an object a particular distance, where force is parallel to the displacement.Sep 9, 2567 BE — To express this concept mathematically, the work W is equal to the force f times the distance d, or ** W = fd**. I

**Energy**

Energy is the “ability to do work, which is the ability to exert a force causing displacement of an object.” In physics, we define energy as the ability of something to do work. Energy can exist in many forms. All forms of energy are either kinetic or potential If work is done faster, power is higher.

**Displacement **

Displacement is the shift in an object's location; it is a vector quantity that includes both direction and magnitude. It represents the straight-line distance moved from the initial point. Displacement is characterized by its size and direction. When an object transitions from point A to point B, its position alters, constituting a change known as Displacement.

**Impulse**

An impulse in biomechanics is the force applied to an object over a period of time, like pushing or hitting something with a certain amount of strength. An impulse is a measure of the force applied for a specific time. Impulse = force x time and has units Ns (Newton seconds). An impulse is the meausre of what is required to change the motion of an object or body and is the product of the force applied over a period of time.

For instance, in the tennis stroke, a significant force applied briefly results in a substantial impact on the momentum of the tennis ball. When kicking a football, if one kicks the football with more force, it will travel at more incredible speeds or a shorter distance of time compared to lightly tapping it with minimum force; the ball will travel less distance in a shorter amount of time.

**Vector Quantity - a quantity which has both a magnitude and a direction**

A quantity with both magnitude and direction; a number, direction, and unit can specify it. An example is a girl riding her bike with a 15km/hr velocity in the southwest direction. Examples of vector quantities are displacement, acceleration, force, momentum, Thrust, pressure, weight, the velocity of light, etc.

**Scalar Quantity **- **a ****quantity**** which only has a magnitude (size)**

Any number that gives the size or magnitude of a quantity, such as degrees or meters. It's a physical quantity described by its magnitude, such as volume, density, speed, energy, mass, temperature and time.

**Magnitude **

Magnitude is the maximum extent of an object's size and direction. It refers to the distance or quantity that defines an entity's size or speed when moving. Magnitude is a unit measurement used to specify the size or intensity of an event; it's defined as the amount by which something out of its usual quantity exceeds another. Magnitude examples include a 10-foot wall or, for instance, Earthquakes, typically measured on the Richter scale, with a magnitude ranging from 1 to 10, indicating their size.

**Mass vs Weight **

Masses' most common calculation formula is M= Volume x Density. Mass is a scalar measurement of the quantity or magnitude of matter in an object; it measures how much matter an object is made of. Mass can be measured in kilograms, or smaller masses can be measured in grams.

Mass stays the same, whereas weight changes depending on the gravity acting on an object. Mass refers to the amount of matter that makes up an object; the SI unit of mass is kilograms. An object's mass does not change at any time except in a nuclear reaction. Unlike weight, mass does not depend on gravity and is constant everywhere; mass can never be zero.

Weight is the measure of the amount of force acting on a mass due to acceleration caused by gravity; it is the measure of the force of gravity acting on a body. The SI unit of weight for weight is newton (N); weight is dependent on gravity, varies from place to place, and can only be zero when there is no gravity-like space. The formula for calculating weight is W = mg, whereby W is the weight of the object, m is the mass of the object, and g is the acceleration due to gravity; on Earth, the value of g is 9.8 / s2.

**Force **

Force is calculated as mass x the acceleration of gravity; Force is a quantity that causes an object to change its motion and direction. Any object, whether at rest, continuously moving, or slowing down to stop, has a force acting on it.

The area under the force vs time graph seen above is given significant attention because it represents the product of force and time, which is also equal to the impulse. Impulse is defined as the change in momentum due to a force.

A force is a push or pull on an object resulting from interacting with another object. Any interaction between two objects generates a force upon each object; when it ceases, the two objects no longer experience the force; force only exists due to interaction.

Force is a vector quantity, meaning it must have a magnitude and direction. To describe the force acting upon an object, you must define its magnitude (size or numerical value) and direction (north, east, south, west, upward or downward, etc).

In biomechanics, force is the action of one object to another. It can be external or internal. Internal forces are the body's responses to external forces. Internal forces consist of muscle, ligament, and joint contact forces. In weightlifting, the barbell is the external force, and the internal force is from the muscles, ligaments, joints, tendons and bones.

External forces arise from the interaction between the human body and its environment. These forces can be categorized as contact forces and non-contact forces, with biomechanics predominantly dealing with contact forces. Contact forces occur when two objects make contact. External forces pull or push on the body from sources outside the body.

**Rate of Force Development (RFD) **

RFD is calculated by dividing the change in force (measured in newtons) by the time taken to achieve that change (measured in seconds), i.e., RFD = Force (newtons) / Time (seconds). It measures the time it takes for an athlete to reach peak force, Which in biomechanics is the most force exerted during a body movement. As seen in the graph below, the peak of the impulse is at the top of the impulse, whereby maximum force is applied during an impulse in the quickest amount of time.

RFD is the best measure of explosive strength; the speed at which the contractile elements of the muscle can develop force is defined as the speed at which the athlete can develop force. Improving your RFD will make you more explosive. You'll be able to develop larger forces in a shorter period of time. RFD is a critical factor in nearly all sports, not just weightlifting, as studies have shown athletes with a higher RFD perform better in physical performance tests. Going back to the theory, all powerful athletes are strong, yet not all strong athletes are powerful.

RFD, down to the nitty-gritty, is the ability of the neuromuscular system (the coordination of our nervous system and muscles; this process enables the control, direction, and movement of the body) to increase the contractile force from a low or resting state whereby muscle activation is performed as quickly as possible. RFD is probably one of the most essential strength tests for athletes and gave way to a new discipline of sports science called 'Velocity Based Training'.

Force is optimally expressed at slower velocities, allowing for the cross-bridges to form.

An example of calculating this is if the lifter produces 440N in 0.5 seconds. The rate of force development would be 8880Ns-1 (440/.05). RDF is measured as the slope of the force-time curve during the initial phase of muscle contraction, usually within a 50-millisecond time interval.

An example would be the above, taking an explosive ballistic-trained athlete (Athlete A), who could be a basketball player, and a heavy resistance-trained athlete (Athlete B), such as a powerlifter. When cross-comparing their force at 200ms, Athlete B can produce greater levels of force in a shorter period than the heavy resistance-trained athlete; however, Athlete B can achieve more maximal force than Athlete A, as seen on the graph.

Athlete A's maximal force peaks and is fixed at what was achieved in 200ms, whereas Athlete B's force continues to increase with each ms but at less rate of force development. Athlete A produces more force in 200ms or 0.2 seconds than athlete B, as seen by the steep slope of their curve.

**Force - Velocity Curve & Relationship**

The force-velocity curve is the relationship between force (f=ma) and velocity (V=d/t). It is displayed on a typical X-y graph as seen above, whereby Force (newtons) is on the Y-axis and Velocity (meters per second) is on the X-axis. Velocity is a vector, as discussed already, and is measured by meters per second, and force is also a vector; thus, its SI (system of units) is newtons, which is the unit of force which gives a mass of 1 kilogram and acceleration of 1 meter per second squared (1 N = 1 kg m s-2).

Therefore, Velocity is the speed of movement measured in meters per second (ms), and force is the measure of power produced to move the object (mass) measured in Newton's. The curve on the F-V Curve graph below shows that the higher the force required, the decrease in velocity is seen. 100% 1RM, which is maximal strength, requires large forces but incredibly slow movement( velocity). On the contrary, speed strength at 40% of 1RM requires less force production but is performed at near maximal velocity.

The force-velocity curve shows a straightforward inverse correlation: as one factor increases, the other decreases simultaneously. It also shows the inverse relationship between force and velocity: as force increases, velocity decreases, and vice versa. It shows a trade-off between force and velocity; a one rep maximum (1RM) max deadlift produces high levels of force but would be lifted at a slow velocity. While a lightweight 30% Deadlift for one repetition moves with rapid velocity as the muscles can contract quicker than a 1RM, less force is needed due to less tension being required to move lighter loads.

Therefore, applying the Force-Velocity curve to weightlifting involves the interaction between the amount of force a weightlifter has to overcome and how fast the barbell is moving. Powerlifting refers to how much weight a lifter is lifting versus how fast the lifter can move the barbell for the squat, bench press, and deadlift exercises.

The biology behind why less force is produced for lighter-load objects lifted at a higher velocity and more force is produced for heavier-load objects at slower velocity speeds is due to the formation of cross-bridges. Cross-bridges are formed at a decreased rate of time with high-velocity, low-force loads compared to low-velocity, high-force loads.

__Cross-bridge Theory__

Cross-bridges are responsible for the movement and force developed during muscle contraction. The myosin heads in the muscle cells alternatively bind to and detach from actin filaments; a cross-bridge is formed when a myosin head attaches to an actin filament.

This cross-bridge formation shortens the sarcomere ( the basic contractile unit of muscle fibre) length, resulting in a contraction. Adenosine triphosphate (ATP) provides the energy for the cross-bridge to form. Immediately after it is formed, the myosin head detaches from the actin filament, breaking the cross-bridge. This process of attachment and detachment is called cross-bridge cycling. Therefore, slower velocity exercises allow the athlete to form more cross bridges and develop more force. Higher velocity exercises provide less time for cross bridges to form and, therefore, result in lower force production.

**Rate of Change (ROC)**

The rate of change formula = R = Δy/ Δx (Change in y divided by change in x). A rate of change is simply how fast something is changing in relation to something else. The rate of change formula gives the relationship describing how one quantity changes in relation to the change in another quantity. To determine the rate of change, you need to divide the difference in one value by the corresponding difference in another value.

An example would be the below chart whereby the rate of change in distance (miles) over time (hours):

**Velocity **

Velocity is the rate of change of an object's position with respect to a frame of reference and time. It describes how quickly an object's position changes in relation to time. It's simply speeding in a specific direction. What differentiates speed and velocity is that velocity considers both the magnitudes of movement and direction, whereas speed only considers the magnitude.

It is a vector quantity, meaning we need both magnitude (speed) and direction to define velocity. The SI unit of velocity is a meter per second (ms-1); if the velocity of an object changes magnitude or direction, then it is said to be accelerating. The equation for calculating velocity is V = d/t, whereby V is velocity, d is displacement, and t is time.

Displacement is defined as the change in position of an object, which has both direction and magnitude.

**Motion**

let's define motion. Motion is the change in position of an object concerning its surroundings in a given interval of time. When we talk about the motion of an object with some mass, it can be described in terms of distance, displacement (change in the position of an object), speed, velocity, time, and acceleration. Newton's three laws of Motion are:

An object at rest remains at rest, and an object in motion stays in motion at a constant speed and in a straight line unless acted on by unbalanced force. I.e. motion or lack of motion cannot change without an unbalanced force acting. If nothing happens to the object or nothing does happen, the object will never go anywhere. If the object goes in a specific direction, it will always go in that direction unless something happens to it. For example, If I throw a baseball straight towards a batter if he misses the ball, it will continue in that specific direction; however, if he hits it, it will change direction.

The acceleration of an object depends on its mass and the amount of force applied. The greater the mass (the amount of matter that makes up an object of the object, the greater the force required to accelerate it. The formula for this is the legendary: F= m x a (force equals mass times acceleration). For example, if you apply force to two objects of different masses, the result will be different accelerations (changes in motion). The object of smaller mass will have more excellent acceleration; the object of the larger mass will have an effect of slower acceleration, whereby acceleration is the effect.

Whenever one object exerts a force on another, the second object exerts an equal and opposite force on the first. This states that for every action (force), there is an equal or opposite reaction (force). Forces are found in pairs; when you sit on a chair, the body exerts the downward force, and the chai needs to exert an equal force upwards to ensure the chair does not collapse under the mass. Acting forces encounter other forces in the opposite direction. A classic example is the cannonball; when it is fired through the air by an explosion, the cannon is pushed backwards, and the force pushing the ball out is equal to that pushing the cannon back.

Relative motion occurs when an object changes its position concerning a reference point in a given time. It is defined as the motion of an object when observed concerning another object, which may be either at rest or in motion. Relative motion refers to determining an object's motion relative to another object's movement, considering its speeds and directions. Take, for example, two cars; Car A is moving west at 30 m / s, and Car B is moving west at 10 m / s/ The relative motion (velocity) of Car A to Car B is given by the difference in their velocities. Therefore, Vad = Va - Vb = 30-10 = 20 m /s.

**Speed**

The equation for speed is Distance travelled divided by time elapsed. Speed is the rate at which an object moves, measured in meters per second, referring to how fast an object moves or the rate at which an object covers direction. For example, the speedometer in the car is scalar, and it has magnitude (the speed at which the vehicle is travelling), but there is no measurement of the direction of travel. If the car was travelling 80 miles in one hour, it was travelling at a speed of 80 Miles/Hour; it does not measure the direction, such as 40 degrees north-west, counterclockwise, etc.

It is a scalar quantity, meaning it has magnitude but not direction. It is defined by its magnitude and size and not direction. Fast-moving objects have high speeds and cover large distances in short amounts of time, while slow-moving objects have low speeds and cover small distances in the same amount of time. An object with no movement at all has zero speed.

Speed pertains to how quickly an object moves; power combines strength and speed. For example, if the car goes 160 mph, speed is how quickly an object moves. So now, let**'**s talk about power and explain what power refers to in physics in detail. In sports science, speed is the ability to move quickly, such as in running, swimming, tennis, or football. It involves stride length and stride frequency.

**Power**

Power, by definition, is the rate of doing work; the equation for power in its simplest form is work divided by time. Power is the ability to exert force quickly and requires producing the most force in the shortest amount of time. Power is how fast a given force moves an object.

Power is the motion that results from force in a given amount of time. A high power value will equal a significant force that creates a relatively large motion. __However, high power doesn’t always result in maximum velocity, and vice versa__. In sports science, athletes' movements are described as high velocity relative to the force they produce or the load they must overcome during the movement.

Movements at slow velocities due to external loads that must be moved may be described as powerful because the velocity is high relative to the force required or mass being accelerated. For example, a powerlifter squatting a 500kg barbell (external load) might have a slow velocity/bar speed; however, a massive amount of power is needed internally to move this load, meaning the velocity was high relative to the 500kg external load and the acceleration required to move this load.

Power is force multiplied by velocity (Power = Force x Velocity), meaning power is not velocity and vice versa; however, improving an athlete's power and velocity can lead to a more explosive athlete. Power is not speed; in sports science, power is related to the athlete's ability to exert maximum force in the shortest amount of time, meaning it is both force and speed, not just one of the two.

Power is developed in sports science by enhancing strength and speed, as power requires both, not just one. This is why you'll commonly see power represented as strength x speed in weightlifting material. Muscle contraction muscle happens at high speed to be powerful,

Now, let's look at the accurate maths for the formula for power; powers' original formula focuses on work as a force times distance and is divided by the time it takes to do that work:

Power = Force * Distance ÷ Time

Now remember that distance ÷ Time is the formula for calculating velocity. Therefore, one can conclude that:

Power = Force * velocity

This formula highlights how important both force and velocity are in generating power; an athlete's ability to produce power isn't solely reliant on physical strength but also on their ability to move quickly.

**Explosive Strength**

So now the question must be asked: What is explosiveness? Using the RFD curve, defined as how quickly the force is developed in the working muscles, we see that maximal strength and heavy loads require a lot of force, as do speed-strength ballistic lighter-load objects. The variant is the velocity speed in m/s.

Therefore, we can consider explosiveness as the maximum value on the curve, i.e. the ability to produce maximum force in minimum time. Hence, the equation for Explosiveness can be expressed as Explosiveness = Fmax / tmax (in newtons per second).

The shorter time value (meters per second) indicates a more explosive motion when considering a force. For example, a 150kg bench press completed in 0.3 seconds is more explosive than a 150kg bench press completed in two seconds. Explosiveness is an internal force or muscle value; it pertains to the internal phenomena within the muscles to produce force against any external object, such as a barbell.

Explosive strength training is complicated. Terminology such as force, power, velocity, and speed training describe and label explosiveness in training. The reason is that Explosive strength training involves them all.

**What’s the Best way to Train Explosive Strength?**

My favorite method is light weight and the use of bands, or as Louie Simmons calls it, the dynamic training method. This single method literally changed Westside Barbell in 1983, and we have refined it for 24 years. Here’s the bullet points on how he explains his method:

This method is used to replace a max effort workout. Submaximal weights are lifted with maximal speed. Remember: F = m x a.

This method indirectly builds strength by increasing a fast rate of force development and explosive strength.

Bands or chains must be used to reduce bar deceleration. Bands will also increase the eccentric phase, which helps build a superior stretch reflex phase.

Reps must be low (1 for pulls, 2 for squats, and 3 for benching). Never go to failure. You must stop if the bar speed decreases.

The bar weight or band or chain resistance must vary to cause a change in metabolic reactions and intramuscular coordination and changes in biometrical variables. This is discussed in The Science and Practice of Strength Training by V. Zatsiorsky. The bar speed must be about 8 meters per second or more.

The sets are no less than 6 and no 90 seconds between sets.

Lifting lighter loads at higher speeds not only builds strength, but it helps prevent injury as well. Other training resources to examine: Special Strengths, Explosive Power Movements, and Plyometrics.

Next up…Strength Endurance!

Accleration

An object is said to be accelerated if there is a change in its velocity. The change in the velocity of an object could be an increase or decrease in speed or a change in the direction of motion. A few examples of acceleration are the falling of an apple, the moon orbiting around the earth, or when a car is stopped at the traffic lights. Through these examples, we can understand that when there is a change in the direction of a moving object or an increase or decrease in speed, acceleration occurs.

What Is Acceleration?

Acceleration is defined as

The rate of change of velocity with respect to time.

Acceleration is a vector quantity as it has both magnitude and direction. It is also the second derivative of position with respect to time or it is the first derivative of velocity with respect to time.__https://byjus.com/physics/acceleration/__

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