Module 5 & 6: Biomechanics of Human Movement Flashcards
Name the 3 Newton’s Laws.
Law of Inertia
Law of Acceleration
Law of Action and Reaction
Describe the Law of inertia.
Objects won’t move unless something makes them move, and they won’t stop unless something stops them
Things stay put unless pushed or pulled.
Describe the Law of acceleration.
The more force you apply to an object, the more it will accelerate, depending on how heavy it is.
The harder you push, the faster it goes.
Describe the Law of action and reaction.
If you push on something, it pushes back with the same force.
For every action, there’s an equal and opposite reaction.
What is force? Give 2 examples.
A push or pull exerted on an object that can cause it to move, stop, or change direction. It is measured in newtons (N) and can affect the motion of objects in various ways.
Pushing a Swing: When you push a swing, the force causes it to move. The harder you push, the faster and farther the swing moves.
Gravity: The force of gravity pulls objects toward the Earth.
What are vectors?
A mathematical quantity that has both magnitude (size / length) and direction.
The length of the arrow shows the magnitude (how big the quantity is).
The direction of the arrow shows the direction of the quantity (which way it’s pointing).
How is force calculated and what is its unit?
Force = Mass × Acceleration:
F = m × a (in Newtons, N)
1 Newton (N) = 1 kilogram meter per second squared (kg·m/s²), which means it is the force needed to accelerate 1 kg of mass by 1 meter per second squared.
What is the difference between one-dimensional and two-dimensional force systems?
One-dimensional force system: forces acting on the same plane and line of action. (A book sitting on a table, gravity is pulls it downward, the table pushes up with equal force.)
Two-dimensional force system: forces acting on the same plane BUT NOT in the same line of action. (A book on a table is being pushed from the side (horizontal force) while gravity pulls it downward (vertical force).
Define coplanar, parallel, orthogonal and concurrent forces.
Coplanar: Forces act in the same plane but in different directions.
(Pushing the book to the right while someone else pushes it at a slight angle on the same plane.)
Parallel: Forces move in the same or opposite directions and are parallel to each other.
(Two people pushing a cart from the same side or opposite sides.)
Orthogonal: Forces are at right angles (90°) to each other.
(Pushing a box sideways while gravity is pulling it down.)
Concurrent: Forces start from the same point, or their paths meet at one point.
(Multiple ropes pulling a hot air balloon from different angles.)
What is a resultant force and how is it calculated?
The overall effect of all forces acting on an object.
The single force obtained by analyzing the force systems.
Collinear (acting along the same line): If acting in the same direction, add the magnitudes; if acting in opposite directions, subtract the smaller force from the larger one.
Coplanar (acting in the same plane but not necessarily along the same line of action): Connect the ends of the vectors to form a parallelogram.
Parallel (parallel to each other in the same or opposite direction): If acting in the same direction, add the magnitudes; if acting in opposite directions, subtract the smaller force from the larger one.
Orthogonal (at right angles): Connect the ends of the vectors to form a parallelogram.
Concurrent (start from the same point): Sum the forces if acting in the same direction.
Define gravity.
The force of attraction that pulls objects toward the center of the Earth.
~10 m/s²
Define centripetal force.
The force that keeps an object moving in a circular path.
Acts perpendicularly (orthogonally) to the object’s velocity and is directed toward the center of the circular path.
To maintain circular motion, a continuous force must be applied to change its direction, preventing it from moving in a straight line.
Carnival ride: the centripetal force is the ride’s wall. It exerts an inward force toward the center of the circle, allowing the people to move in a circular path instead of flying outward as the ride spins. what keeps people pressed against the outer wall of the ride as it spins.
Define friction.
A force that occurs between two surfaces in contact, resisting movement. It tries to stop or slow down moving objects. It always acts in the opposite direction to the movement. If you push an object to the right, it pulls to the left.
Static Friction: occurs when two surfaces are not moving relative to each other. It prevents motion until enough force is applied.
Dynamic (Kinetic) Friction: occurs when surfaces are already moving against each other. It resists further movement.
Define elastic force.
The force exerted by an elastic material when it is deformed (stretched or compressed) by an external force.
Elastic Materials: are objects that can change shape when a force is applied but return to their original shape when the force is removed.
Direction of Force: The elastic force typically acts in the opposite direction to the deformation, meaning the material tries to return to its original shape.
Deformation: How much a material deforms (changes shape) depends on the load (force) applied and the material’s stiffness. Stiff materials resist deformation more than flexible ones.
Human Body Example: Different body parts have different stiffness. Muscles can stretch more easily than ligaments. When forces act on the body (like during movement), these parts respond differently based on their stiffness.
Load Direction: Body parts endure loads in various directions, and they resist these loads in different ways depending on their structure.
Define ground reaction force.
The force the ground exerts back when you apply a force to it, following Newton’s 3rd Law (every action has an equal and opposite reaction).
Standing: Your body pushes down on the ground (gravity, your weight), and the ground pushes up with an equal force, keeping you balanced and upright.
Jumping: You push down on the ground, and it pushes you back up, helping you jump.
Running: As your foot hits the ground, it pushes back both upwards (to support your weight) and forwards (to help you move forward).
Wall Push-ups: You push against the wall, and the wall pushes back with equal force, allowing you to push yourself away from it. This is like ground reaction force, but from a wall.
What factors will influence the amount of deformity suffered by an object?
Type of Material:
Elastic Materials: can be stretched or compressed and will return to their original shape once the force is removed.
Non-Elastic Materials: may not return to their original shape after being deformed
Applied Load: the size and direction of the force applied to the object affects how much it deforms. A greater load typically results in more deformation.
Material Stiffness: refers to how resistant a material is to deformation. Stiffer materials deform less under the same load.
Direction of Load: different body parts experience loads from various directions, and their ability to resist deformation varies. Muscles and ligaments respond differently when stressed.
Duration of Load: the length of time a force is applied can impact deformation. Continuous loading may lead to more significant deformation, especially in viscoelastic materials.
What is moment or torque?
The turning force that results from applying a force at a distance from a pivot point or axis of rotation.
A tire ratchet, as an example.
How is moment calculated?
Moment = Force x Distance
The further from the axis, the easier to cause moment/torque.
What is the definition of a lever?
A rigid bar that rotates around a fixed point aka fulcrum
Describe the differences between the 3 types of levers that can be found in the human body.
Based on the arrangement of force, axis and resistance causing variations in force, speed, and ROM.
Type 1: Axis in the middle; See-saw; can be MA or MD
Type 2: Resistance in the middle; Wheelbarrow; MA
Type 3: Force in the middle; Sweeping; MD
Give one example of type 1, type 2 and type 3 levers found in the human body.
First-Class Lever: Neck extension
Force: Splenius capitis insertion
Axis: Atlanto-occipital joint
Resistance: Weight of the skull and surrounding tissues
Second-Class Lever: Calf raises
Axis: MTP joint
Resistance: Body weight
Force: Achilles tendon insertion
Third-Class Lever: Bicep curl
Resistance: Forearm weight, external load
Force: Biceps brachii insertion
Axis: Elbow joint
How would you define mechanical advantage in the human body?
The efficiency a lever system can move a load.
The ability of muscles and joints to amplify force and move a heavier load with less effort by using optimal leverage.
A lever that has mechanical disadvantage <1 will likely have a speed advantage. Can you explain this statement?
Speed advantage is a lever system with a mechanical disadvantage. Speed advantage enables faster movement by requiring more effort to move a shorter distance while moving the load over a greater distance.
This is beneficial for tasks requiring quick, powerful movements, such as throwing or swinging.
What is the difference between linear and angular motion?
Linear motion (translation): The object moves in a straight or curved path.
Angular motion (rotation): The object rotates around a fixed point or axis.
LM: Displacement refers to the shortest distance between two points.
AM: Displacement is measured in degrees (e.g., one full rotation = 360°).
LM: Velocity and acceleration are measured in m/s and m/s² when a force is applied directly through the object’s center, moving it in a straight line (e.g., billiard balls moving in a straight path).
AM: velocity and acceleration are measured in °/s and °/s².
Define Centre of Gravity.
The point where an object’s entire weight is concentrated. It is a geometrical concept used to describe the average location of an object’s weight distribution.
Define Centre of Mass.
The point where the mass of an object is evenly distributed in all directions. It is the balance point of the object, where if supported, the object would remain in equilibrium regardless of its orientation.
Define Line of Gravity.
The vertical line that represents the direction of gravitational pull, extending from the COG down to the ground. It indicates where the weight of the object acts and is essential for understanding stability and balance.
Define Base of Support.
The area beneath an object that includes all points of contact with the ground. It is the surface area that supports the weight of the body and provides stability.
What is the definition of balance?
The COG of an object remains within its BOS, allowing it to maintain an upright position without falling.
What is the definition of stability?
The ability of a body to maintain or return to its initial state of balance after a disturbance. It reflects how well an object resists tipping or losing equilibrium.
What is muscle work and how is it calculated?
The ability of a muscle to produce movement by exerting force.
Muscle Work = Muscle Force x Muscle Length Change
Concentric contraction = positive work
Eccentric contraction = negative work
Isometric contraction = zero work
What is potential energy (Ep) and what is it dependent on?
The energy an object possesses due to its position in a gravitational field.
Dependence:
Mass: The greater the mass of the object, the more potential energy it has.
Gravity: The acceleration due to gravity (usually 9.81 m/s² on Earth).
Height: The height of the object relative to the ground.
Ep = Mass × Gravity × Height
If gravity = 0, the object has no potential energy.
What is kinetic energy and what is it dependent on?
The energy that an object possesses due to its motion.
Dependence:
Mass: Kinetic energy increases with an increase in mass.
Velocity: The speed of the object; kinetic energy is proportional to the square of the velocity.
Ek = ½ × Mass × Velocity(squared)
The faster an object moves, the higher its kinetic energy.
What is elastic energy and what is it dependent on?
The energy stored in an object when it is deformed (stretched or compressed spring) from its original shape.
Dependence:
Stiffness (k): A measure of how much the material resists deformation; greater stiffness results in less deformation and less elastic energy.
Deformation/displacement (x): Stiffness constant of the material (measured in newtons per meter, N/m).
Change in Length (ΔL): The amount of deformation experienced by the material.
Es = ½ kx(squared) OR Es = k × ΔL
The less stiff the material, the more it will deform and produce greater elastic energy
Name 3 principles of energy conservation.
Sum of energy is constant (air in a sealed container is constant)
Transformation of energy forms (electricity becomes light)
Not created nor Destroyed (recycles)
What is hydrostatic pressure?
The pressure exerted by a fluid at rest due to the weight of the fluid above it. This pressure acts in all directions, pushing against any object immersed in the fluid.
Related to the weight of the fluid (increased pressure with increased depth)
What is the density of the human body? Will it have the tendency to float or sink when immersed in clean water?
Density (D) defined as the mass (𝑀) of an object divided by its volume (𝑉).
The density of the human body is generally less than 1 g/cm³, the human body will tend to float when immersed in clean water.
D = M / V
What is buoyancy?
The upward force exerted by a fluid on an object that is immersed in it. This force opposes the weight of the object, helping it to float.
Archimedes’ Principle: any body immersed in a fluid experiences an upward force equal to the weight of the fluid it displaces.
Proportionality: The buoyant force is proportional to the volume of fluid displaced. Meaning larger bodies displace more fluid and experience a greater upward force.
In which condition would a body immersed in water have the tendency to rotate?
When the COG and the COB do not align.
This misalignment creates a moment about the axis, causing the body to rotate until the COG and COB line up.
The greater the distance between the COG and COB, the larger the moment arm and the more pronounced the tendency to rotate.
What is flow and how can it affect movement in water?
Refers to the movement of a fluid (such as water) from one point to another, typically due to a difference in pressure.
Laminar Flow: Smooth and regular movement of fluid.
Turbulent Flow: Chaotic and irregular fluid movement, with swirling currents.
LF: The fluid moves in parallel layers with minimal disruption between them. Creates less resistance to an object moving through it.
TF: Increases resistance against an object moving through it, making movement more difficult.
LF: Objects will experience less resistance, making movement smoother and easier.
TF: Objects will experience more resistance, making movement difficult and requiring more effort.
Flow can be used in therapeutic settings. LF can facilitate smoother movement for injury recovery. TF can be used to increase resistance for strength training or to challenge balance in aquatic exercises.
When would you need to calculate force?
When determining how much push or pull is needed to move an object, accelerate it, or overcome resistance
F=m*a
(Force equals mass times acceleration)
When would you need to calculate mass?
When you need to know how much matter is in an object or when analyzing motion and you already know what force is applied to an object and its acceleration
m= F / a
(Mass equals force divided by acceleration)
When would you need to calculate the mechanical advantage?
When analyzing the efficiency of a lever to determine how much a lever amplifies an input force to move a load.
MA = force arm / load arm
When would you need to calculate work?
when determining how much energy is transferred by a force moving an object over a distance for analyzing energy use in physical systems or tasks
W=F*d
(Work equals force times displacement)
When would you need to calculate for moment of inertia?
When analyzing rotational motion to understand how an object’s mass distribution affects its resistance to changes in rotational speed for studying angular momentum
I=m×r 2
(Inertia equals mass times the distance from the axis of rotation)
When would you need to calculate for potential energy?
When assessing the energy stored in an object due to its position or height in a gravitational field
Ep = mass * gravity * height
or PE = mgh
When would you need to calculate kinetic energy?
When determining the energy an object possesses due to its motion in analyzing the motion of moving objects, understanding energy transformations, and solving problems related to collisions and impacts.
Ek = 1/2 mass * velocity 2
(Kinetic energy equals half the mass times velocity squared)
When would you need to calculate elastic potential energy?
When determining the energy stored in a spring or elastic material due to its deformation
Es = 1/2 K*ΔLength squared
When would you calculate for Hooke’s Law?
When determining the restoring force exerted by a spring when it is compressed or stretched
Es = k*ΔLength
