Newtons Laws Part 1
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Questions and Answers

What does Newton's First Law of Inertia state about an object at rest?

  • It will start moving spontaneously after a period of time.
  • It will move in a circular motion unless acted upon by an external torque.
  • It will remain at rest unless acted upon by a net external force. (correct)
  • It will eventually accelerate if unbalanced forces act upon it.

Which statement best describes the term 'inertia'?

  • It refers to the speed of an object in motion.
  • It is the capability of an object to maintain constant speed regardless of mass.
  • It is the force required to change an object's state of motion.
  • It represents an object's resistance to a change in velocity. (correct)

In terms of motion, what is required to change the state of an object in linear motion according to Newton's laws?

  • An external force is necessary. (correct)
  • Friction is sufficient to change its state of motion.
  • No force is required if the object is already in motion.
  • Only constant acceleration is required.

What is the relationship between inertia and mass?

<p>Inertia is proportional to mass. (C)</p> Signup and view all the answers

Which of the following scenarios best illustrates Newton's Third Law of action-reaction?

<p>A person jumps off a small boat, causing the boat to move backward. (B)</p> Signup and view all the answers

Which statement best describes the relationship between net force and mass in the context of Newton's Second Law?

<p>Net force is directly proportional to the acceleration and inversely proportional to mass. (A)</p> Signup and view all the answers

Which of the following correctly describes what happens when two objects interact concerning their masses?

<p>The reaction experienced by each object is proportional to their respective masses. (D)</p> Signup and view all the answers

What does the term 'ground reaction force' specifically refer to?

<p>The force exerted by the ground in response to the weight of an object. (A)</p> Signup and view all the answers

In the context of Newton's Second Law, how does mass affect acceleration?

<p>Acceleration is inversely proportional to mass. (C)</p> Signup and view all the answers

What role does co-contraction play in joint reaction force?

<p>Co-contraction minimizes the opposing forces at a joint. (A)</p> Signup and view all the answers

What effect do the hamstrings have on the anterior translation of the tibia in relation to the femur?

<p>The hamstrings pull the tibia posteriorly. (C)</p> Signup and view all the answers

In static equilibrium, what can be said about the vertical velocity and net force?

<p>Vertical velocity is zero, and net force is zero. (B)</p> Signup and view all the answers

What happens to the force of air resistance when the parachute opens during a fall?

<p>Air resistance becomes much greater than gravity. (D)</p> Signup and view all the answers

What is primarily responsible for the co-activation of the hamstrings and quadriceps during movement?

<p>To decrease the need for force from the ACL. (D)</p> Signup and view all the answers

In dynamic equilibrium during free fall, what must be true about the forces acting on the falling body?

<p>Gravity and air resistance are equal and opposite at constant velocity. (A)</p> Signup and view all the answers

Which of the following best describes the motion of an object when it has a large moment of inertia (I) and small angular velocity (ω)?

<p>It rotates slowly due to high resistance to changes in motion. (A)</p> Signup and view all the answers

What occurs during the first jump out of a plane in regard to gravitational forces?

<p>Gravity exceeds air resistance, leading to acceleration. (A)</p> Signup and view all the answers

Which situation represents a state of static equilibrium?

<p>An object at rest with no net force acting on it. (D)</p> Signup and view all the answers

What is the primary factor that determines the moment of inertia of an object?

<p>The distribution of mass relative to the axis of rotation (A)</p> Signup and view all the answers

In dynamic equilibrium, which of the following statements is incorrect?

<p>The object is at rest (D)</p> Signup and view all the answers

Given the equation for torque ($τ = Iω$), what does a large moment of inertia imply about an object's angular acceleration?

<p>The angular acceleration is slow (D)</p> Signup and view all the answers

In static equilibrium, which scenario is not a requirement for a body?

<p>Net forces acting on the body are nonzero (C)</p> Signup and view all the answers

Which statement best describes the relationship between mass moment of inertia and angular acceleration in a diving scenario?

<p>A diver's position affects their mass moment of inertia and thus their angular acceleration (C)</p> Signup and view all the answers

What condition must be met for an object to accelerate according to Newton's Second Law?

<p>The sum of forces acting on the object is nonzero (C)</p> Signup and view all the answers

Which of the following statements about air resistance in a falling context is false?

<p>Air resistance affects only linear motion, not rotational motion (B)</p> Signup and view all the answers

Which scenario best illustrates the concept of static equilibrium?

<p>A book resting on a table (C)</p> Signup and view all the answers

Flashcards

Inertia

The tendency of an object to resist changes in its motion.

Newton's First Law (Law of Inertia)

An object at rest will stay at rest, and an object in motion will stay in motion at a constant velocity, unless acted upon by a net external force.

Inertia (Quantitative Definition)

The measure of an object's resistance to changes in its linear velocity.

Force (Linear Motion)

The force required to start, stop, accelerate, or decelerate linear motion.

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Torque (Rotational Motion)

The torque required to start, stop, accelerate, or decelerate rotational motion.

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Moment of Inertia

A measure of an object's resistance to changes in its rotational velocity. It depends on both the object's mass and how that mass is distributed.

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Static Equilibrium

A state where the object is not moving and has no net forces acting on it.

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Dynamic Equilibrium

A state where the object is moving at a constant velocity and has no net forces acting on it.

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Torque

The force needed to spin an object. It's like the rotational equivalent of force in linear motion.

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Angular Acceleration

Rotational acceleration: It describes how quickly an object's rotational speed changes.

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Newton's Second Law for Rotational Motion

This is the relationship between torque, moment of inertia, and angular acceleration. It's the rotational version of Newton's Second Law: F=ma

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Factors Affecting Moment of Inertia

The moment of inertia is larger when the mass is spread out from the center of rotation. When the mass is closer to the center, the moment of inertia is smaller.

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Net Force

The force that causes an object to accelerate, measured in Newtons (N). It is the product of mass and acceleration: ΣF = ma.

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Acceleration

The rate of change of velocity over time. It is measured in meters per second squared (m/s²).

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Ground Reaction Force

A special type of force that acts on an object when it is in contact with a surface. It is equal in magnitude and opposite in direction to the force applied to the surface.

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Joint Reaction Force

The force that acts between the surfaces of a joint, helping to stabilize and control movement. It is usually the difference between the muscle force and external force.

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ACL Function

The anterior cruciate ligament (ACL) prevents the tibia from sliding forward relative to the femur.

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Hamstring Role in ACL Support

Hamstrings help the ACL by pulling the tibia backwards, reducing the load on the ACL.

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Moment of Inertia (I)

Moment of inertia (I) is a measure of an object's resistance to changes in its rotational motion.

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Angular Velocity (ω)

Angular velocity (ω) is the rate at which an object rotates.

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Relationship between I and ω

An object with a large moment of inertia (I) rotates slowly (small angular velocity, ω), while an object with a small moment of inertia (I) rotates quickly (large angular velocity, ω).

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Inverse Proportional Relationship between I and ω

The relationship between moment of inertia (I) and angular velocity (ω) is inversely proportional: as one increases, the other decreases.

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Study Notes

Movement Science Session II: Newton's Laws

  • Objectives include describing force, motion, levers and biomechanical components, applying kinesiological principles of kinematics and biomechanics to movement dysfunction, and analyzing kinetic and kinematic factors influencing movement.

Perspective

  • A Family Guy cartoon image is used as a visual aid.

Laws Governing Motion

  • Newton's Laws are presented:
    • First Law (Inertia): Objects at rest stay at rest, objects in motion stay in motion (with constant velocity) in a straight line unless acted upon by a force. Linear motion requires force: to start, stop, accelerate, and decelerate. Rotational motion requires torque: to start, stop, accelerate, and decelerate.
    • Second Law: The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The acceleration takes place in the same direction as the net force or torque.
    • Third Law (Action-Reaction): For every action, there is an equal and opposite reaction. When two objects interact, each experiences a force that is dependent on its mass.

Newton's First Law: Law of Inertia

  • Inertia is the resistance of an object to a change in its velocity. Linear inertia is proportional to mass, and measured in the same units as mass (e.g., kg). Rotational inertia is proportional to both mass and the distribution of that mass (m*r²).

Equilibrium

  • Static Equilibrium: No linear or rotational acceleration (body is stationary. The sum of forces in all directions (ΣFx = 0, ΣFy = 0) and the sum of torques (Στ=0) are zero.
  • Dynamic Equilibrium: Constant linear or rotational velocity. The sum of forces (ΣFx = 0, ΣFy = 0) and the sum of torques (Στ=0) are zero. No acceleration.

Newton's Third Law

  • For every action, there is an equal and opposite reaction.
  • When two objects interact, the forces each experience are dependent on their mass.
  • Applications include ground reaction force, and joint reaction force.

Ground Reaction Force

  • The force exerted by the ground on the body, equal in magnitude and opposite in direction to the force the body applies to the ground.

Joint Reaction Force

  • The force between the surfaces of a joint, developing in reaction to other forces.
  • It's usually the difference between muscle forces and external forces. This difference can cause acceleration or deceleration effects.

Opposing Forces: Co-Contraction

  • Co-contraction (activation of opposing muscle groups) helps control joint movement during tasks.
    • The quadriceps pull the tibia anteriorly and the hamstrings pull the tibia posteriorly. This coordinated action reduces the force on, and thereby provides increased stability for the ACL.

Demonstrations/Visual Aids

  • The notes include various demonstrations(visual aids) to explain the concepts, including a video link. Some of these may display scenarios like a person jumping out of an airplane and the effects of gravity and air resistance.

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