KNES 361 - Linear Kinetics I and II

What area of biomechanics studies the causes of motion, including forces, mass, and acceleration?

Linear Kinetics

Simply put, what is a force?

A pushing or pulling action.

What effect does a force have on an object's motion?

It causes acceleration.

What is the standard unit of force?

Newton (N)

Express 1 Newton (N) in terms of base metric units (kg, m, s).

1N = 1 kg * m/s^2

Approximately how many pounds-force (lb) are in 1 Newton (N)?

0.225 Ibf

Approximately how many Newtons (N) are in 1 pound-force (lbf)?

4.45 N

According to Newton’s 2nd Law, the acceleration of an object is proportional to the _____ applied.

Net force

How is the Net Force (FNet) determined when multiple external forces are acting on a system?

By calculating the vector sum of all external forces.

Newton’s 2nd Law states that acceleration depends directly on the net force and _____ on the mass.

Inversely

If the applied force acting upon an object is increased while mass remains constant, what happens to acceleration?

Acceleration increases.

If the mass of an object is increased while the applied force remains constant, what happens to acceleration?

Acceleration decreases.

Newton’s 3rd Law of Motion is also known as the Law of _____.

Action-Reaction

How does Newton’s 3rd Law explain the force applied by the ground during a jump?

The ground applies an equal and opposite reaction force to the force applied by the feet.

In biomechanics, what does the acronym GRF stand for?

Ground Reaction Force

What are the three essential characteristics of a force vector?

Magnitude, point of application, and line of action.

In human muscle mechanics, what represents the 'Point of Application' for a force vector?

The attachment of the muscle to the bone.

In human muscle mechanics, what represents the 'Line of Action' for a force vector?

The action or pull of the muscle.

What term describes force vectors that all act along the same line of action?

Collinear Forces

What term describes force vectors that act through the same point but not along the same line?

Concurrent Forces

How are concurrent forces added to determine the net force?

The x and y components are added separately.

When calculating the resultant of concurrent forces, what formula is used to find the magnitude (FNet)?

a^2 + b^2 = c^2 (Pythagorean theorem)

When calculating the angle (theta) of a resultant force from its components, which trigonometric function is used?

tan^-1 (opp/adj)

What state occurs when an object has zero acceleration because the net force acting on it is zero?

Static Equilibrium

What are the two mathematical requirements for a system to be in static equilibrium?

sum Fx = 0 and sum F_y = 0.

What type of sketch is used to analyze all the effects of force vectors acting on a body or system?

Free Body Diagram (FBD)

To study human movement, which type of forces (Internal or External) are primarily analyzed?

External forces

Why might a biomechanist study internal forces rather than external forces?

To understand how injuries (like ACL tears) occur within the body.

What is the specific formula for Weight (W) on Earth?

W = mg

What is the standard value for acceleration due to gravity (g) on Earth?

-9.81 m/s^2

True or False: Weight and mass are the same thing.

False (Weight is a force, mass is the quantity of matter).

What instrument is commonly used in a biomechanics lab to measure Ground Reaction Forces?

A Force Plate

During running, the peak vertical GRF is typically _____ times an individual's body weight.

2-3

During landing, the peak vertical GRF can reach _____ times an individual's body weight.

7-10

What force acts between and parallel to two surfaces in contact and always opposes relative motion?

Friction

What are the two sub-types of dry (solid-to-solid) friction?

Static friction and Kinetic friction.

What are the two sub-types of fluid friction?

Air resistance and Water resistance.

In the formula F_f = u F_N, what does u(mu) represent?

The Coefficient of Friction.

In the formula F_f = mu F_N, what does F_N represent?

The Normal Force.

How is the Normal Force (F_N) defined relative to the contact surface?

It is the force acting perpendicular to the surface.

Which material combination has a lower coefficient of friction: rubber on a floor or cartilage on cartilage?

Cartilage on cartilage (mu = 0.005).

How does a rock climber increase friction between their feet and a rock face?

By leaning away from the face to increase the normal force.

In sports, pine tar and rosin are used to _____ friction.

Increase

What term refers to the quantity of motion of a system, calculated as the product of mass and velocity?

Linear Momentum (M)

What is the mathematical formula for linear momentum?

M = mv

What are the standard units for Linear Momentum?

kg * m/s

What physical quantity is defined as a force acting over a specific time interval (Ft)?

Impulse

According to the Impulse-Momentum Theory, what does an external impulse cause?

A change in momentum (Delta M).

How can Impulse be determined from a Force-Time Curve?

By calculating the area under the curve.

In a vertical jump, what does the area under the force-time curve that exceeds body weight represent?

The Push-Off Impulse.

In physics, how is Mechanical Work (W or U) calculated?

Work = Force times Displacement (W = Fd)

What is the standard unit for Work?

Joules (J)

One Joule (J) is equal to one _____.

Newton-meter (Nm)

During a bench press, work is _____ on the upstroke.

Positive

During a bench press, work is _____ on the downstroke.

Negative

When is mechanical work considered negative in muscle activity?

When a muscle absorbs energy during an eccentric contraction.

What is the rate at which work is done called?

Mechanical Power (P)

What is the standard unit for Mechanical Power?

Watts (W)

One Watt (W) is equal to one _____.

Joule per second (J/s)

Besides Work/Time, what is the alternative formula for Power using force and velocity?

P = Fv

In sports, the most powerful athlete is often the one who can generate a combination of high force and high _____.

Velocity

How is Mechanical Energy defined?

The capacity to do work.

What are the two primary forms of mechanical energy?

Kinetic Energy (KE) and Potential Energy (PE).

What form of mechanical energy is due to an object's motion?

Kinetic Energy (KE)

What is the formula for Translational Kinetic Energy?

KE = ½ * mv^2

What form of mechanical energy is due to an object's position (height)?

Potential Energy (PE)

What are the two specific types of Potential Energy mentioned in biomechanics?

Gravitational and Strain.

What is the formula for Gravitational Potential Energy?

PE = mgh

According to the Work-Energy Relationship, what is created when Work is done?

Energy

During the upward flight of a thrown ball, Kinetic Energy decreases while Potential Energy _____.

Increases

During the downward flight of a ball, Potential Energy decreases while Kinetic Energy _____.

Increases

When a ball is at its maximum height after being thrown, what is its Kinetic Energy (KE)?

Zero (0)

In landing mechanics, energy is absorbed through _____ work.

Negative

How can an athlete land with a smaller impact force while performing the same amount of work?

By increasing the 'give' or distance (d) over which the force is applied.

In a pole vault, work is done to increase the athlete's _____ energy as they rise over the bar.

Potential

What happens to the total mechanical energy (PE + KE) of a ball in flight if air resistance is ignored?

It remains constant.

Identify the type of friction: a resistance to motion between a solid object and water.

Fluid friction

Why is synovial fluid important in human joints?

It decreases the coefficient of friction between articulating bones.

What is the 'motive' force that propels the body forward during walking?

Friction

In the context of the high jump, which force creates upward vertical velocity at takeoff?

Ground Reaction Force (GRF)