pty1016 kinetics

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Questions and Answers

Which principle describes that an object in motion continues in its state of motion unless acted upon by an external force?

Inertia (correct)

Acceleration due to gravity

Law of Action-Reaction

Law of Acceleration

According to Newton's Second Law, what happens to the acceleration of an object when the force applied is doubled?

It remains constant.

It doubles. (correct)

It becomes zero.

It increases by half.

Which of the following correctly describes the concept of reaction forces?

Reaction forces are equal in magnitude and opposite in direction to the action force. (correct)

Reaction forces only occur when two objects are in motion.

Reaction forces exist only during collisions.

Reaction forces are always greater than the action forces.

What is the first step in constructing a free body diagram?

Identify and isolate the free body. Signup and view all the answers

In a free body diagram of a right arm holding a ball, which force represents the weight of the ball?

Ball weight (B) Signup and view all the answers

What does the term 'ground reaction forces' refer to during walking or running?

The natural resistance of the ground against the body. Signup and view all the answers

What is the purpose of establishing a coordinate reference frame in physics?

To simplify the calculation of forces. Signup and view all the answers

Which of the following describes dynamic equilibrium?

An object moves in a straight line at a constant speed. Signup and view all the answers

What is the correct mathematical expression for impulse?

Impulse = F ∆ t Signup and view all the answers

If a man's mass is 65 kg and his velocity at takeoff is 3.4 m/s, what is the change in momentum?

221 kg∙m/s Signup and view all the answers

What is the relationship between work and displacement in the context of mechanical work?

Work is the product of force and displacement in the direction of the applied force. Signup and view all the answers

How is power defined in the context of mechanics?

Power is the rate of doing work. Signup and view all the answers

Which of the following statements is true regarding positive and negative work?

Isometric contraction involves no mechanical work despite muscle effort. Signup and view all the answers

If an impulse is 221 N ∙ s and is applied over a time of 0.2 seconds, what is the force applied?

1,105 N Signup and view all the answers

During which type of contraction is work done equal to zero?

Isometric contraction Signup and view all the answers

What unit is used to express impulse?

N∙s Signup and view all the answers

What does the internal moment arm (IMA) represent in the context of muscle force?

The perpendicular distance between the axis of rotation and the Y component of muscle force. Signup and view all the answers

Which method can be used to compose nonparallel, coplanar force vectors?

The parallelogram method. Signup and view all the answers

In the X-Y coordinate reference frame, what does the direction of the thin black arrowheads indicate?

The positive directions of the X and Y axes. Signup and view all the answers

In the context of isometric knee extension, which forces are represented in the free body diagram?

Internal force, external force, and joint reaction force. Signup and view all the answers

Which component of the muscle force is represented as the vertical vector in the force resolution?

The Y component (M Y ). Signup and view all the answers

What force is indicated by 'S' in the context of the knee extension exercise?

The weight of the shank-and-foot segment. Signup and view all the answers

What is typically true about the placement of force vectors when using the polygon method?

Vectors are arranged tip-to-tail to illustrate resultant forces. Signup and view all the answers

Which of the following statements about torque in the context of muscle forces is accurate?

The internal torque produced by a muscle is determined by both muscle force and moment arm. Signup and view all the answers

How does the angle-of-insertion of the biceps muscle affect torque during elbow movement?

It changes the X and Y components of the muscle force. Signup and view all the answers

At which angle-of-insertion does the biceps muscle generate the maximal internal torque?

90 degrees Signup and view all the answers

What is the effect of changing the angle of the elbow joint on the internal moment arm?

The internal moment arm is constant throughout all joint angles. Signup and view all the answers

If the magnitude of the muscle force is constant at 120 N, what primarily changes during different joint angles?

The Y component of the muscle force fluctuates significantly. Signup and view all the answers

In the context of torque generation in the elbow joint, what is primarily defined by the angle-of-insertion?

The proportions of the X and Y forces. Signup and view all the answers

What remains unchanged despite the variation in joint angles?

The internal moment arm. Signup and view all the answers

Which joint angle would result in the least effective muscle force application?

15 degrees Signup and view all the answers

What is the primary consequence of altering the angle of insertion in muscle mechanics?

Changing the internal torque throughout motion. Signup and view all the answers

What occurs when two forces act in different directions from the same point?

They create a resultant vector composed of rotation and either compression or distraction. Signup and view all the answers

In which scenario would the resultant force be larger than the individual forces applied?

When the rotational and distraction forces are nearly equal but act in different directions. Signup and view all the answers

What is the effect of a force vector that is applied perpendicularly to a lever?

It results in no distraction or compression force, only rotation. Signup and view all the answers

What shoulder motion results from resolving the forces generated by the clavicular and sternal portions of the pectoralis major muscle?

Adduction or shoulder flexion depending on the force direction. Signup and view all the answers

In which anatomical position does a constant muscle contraction yield the most force for arm elevation?

With the arm bent at 90 degrees at the elbow. Signup and view all the answers

What does the center of gravity (CG) represent in relation to an object or body?

The point around which all gravitational forces are balanced. Signup and view all the answers

How does increasing the moment arm (MA) affect muscle force production?

It decreases the muscle force required to produce the same torque. Signup and view all the answers

Why might two forces that are equal in magnitude and opposite in direction result in a larger resultant force when applied at an angle?

They produce a rotational effect that amplifies the resultant vector. Signup and view all the answers

Study Notes

Newton's Laws

Newton's First Law of Motion (Inertia): An object in motion will stay in motion and an object at rest will stay at rest unless acted upon by an external force. This principle underlines the concept of inertia, where the natural tendency of an object is to maintain its current state, whether it is at rest or in uniform motion. Inertia is proportional to an object’s mass; greater mass means greater inertia, which makes it harder to change the object's state of motion. The law emphasizes the importance of external forces and how they influence the movement of objects.
Newton's Second Law of Motion (Law of Acceleration): Acceleration of an object is directly proportional to the force applied and occurs in the direction of the force. This law can be mathematically expressed as F = ma, where F is the total force acting on the object, m is the mass of the object, and a is the acceleration. This formula highlights that the greater the force applied to an object, the more it will accelerate, while a heavier object requires more force to achieve the same acceleration compared to a lighter object. This relationship is crucial in understanding how different factors influence motion.
- Force is measured in Newtons (N), which is defined as the amount of force required to accelerate a one-kilogram mass by one meter per second squared. This unit connects force with mass and acceleration, providing a standardized way to quantify the effects of forces in motion.
Newton's Third Law of Motion (Law of Action-Reaction): For every action, there is an equal and opposite reaction. This law explains the interactions between two bodies and dictates that the forces two objects exert on each other are always equal in magnitude and opposite in direction. For example, if a person pushes against a wall with a certain force, the wall pushes back against the person with an equal force in the opposite direction. Understanding this law helps in analyzing a variety of physical interactions, from walking to rocket propulsion.
- When one body exerts force on another, the second body exerts an equal and opposite reaction force. This mutual interaction is fundamental in all types of forces, including gravitational force, contact forces, and friction. The concept of action and reaction illustrates the inherent balance in nature where forces always act in pairs.

Impulse-Momentum Relationship

Impulse is the change in momentum of an object, illustrating how the application of force over time affects an object's motion. In physical terms, momentum is described as the product of an object's mass and its velocity (p = mv), indicating that an object in motion carries momentum. The impulse experienced by an object can change its momentum, leading to changes in velocity and direction.
- Impulse = Force x Time, a formulation derived from Newton's second law, shows how force applied over a time interval results in an overall effect on momentum. This emphasizes the critical role of the duration of force application in achieving desired changes in motion.
- Impulse = Change in momentum (mass x velocity), which confirms that the total change in momentum is equal to the impulse applied to the object. This relationship is essential in various real-world applications, such as in sports and vehicle collisions, where understanding how forces act over time can aid in safety analysis.

Work, Power, and Energy

Work is defined as the product of force and displacement in the direction of the force: the concept recognizes that energy is transferred when a force causes an object to move. Work is crucial in understanding how energy is applied and transformed in various systems.
- Work = Force x Displacement, which means the direction of movement must align with the force applied for work to be done. If an object does not move or the force is perpendicular to the direction of motion, no work is done.
Positive work occurs when the force and displacement are in the same direction. This typically results in an increase in the energy of the system, causing objects to speed up or lift against gravity.
Negative work occurs when the force and displacement are in opposite directions. This usually results in a reduction of the system's energy, such as when a person slows down or stops a moving vehicle, where friction acts in the opposite direction of motion.
Power is defined as the rate of doing work: it illustrates how quickly energy is generated or transferred in a system, providing insight into efficiency and performance in mechanical and physical processes.
- Power = Work / Time, which indicates that the amount of work done over a specified period reflects the system's power output. This relationship is particularly important in fields such as engineering, where optimal power usage can significantly influence design and performance parameters.

Torque

Torque is the rotational force that causes an object to rotate around an axis or pivot point. It represents a twisting force that can change an object’s angular motion and is crucial in applications involving gears, levers, and wheels.
- Torque can be calculated using the formula: Torque = Force x Moment arm, where the moment arm is the perpendicular distance from the axis of rotation to the line of action of the force. This relationship highlights that greater distance from the pivot point increases the torque effect, making it easier to cause rotation.
- Internal Torque: This is torque generated by muscles during movement, essential in biomechanics and physical activities. Internal torque accounts for how muscles work together to produce movement at joints and how they balance with external forces.
- External Torque: This is the torque generated by forces such as gravity or friction acting on an object, influencing its motion in conjunction with internal forces. Understanding external torque is key in sports science, machinery operation, and physical dynamics.
Moment Arm: The concept states that the longer the moment arm, the greater the torque for a given force. This principle is significant in mechanics and ergonomics, as it helps optimize lever systems in tools and machinery design, enabling greater efficiency and effectiveness.

Centre of Gravity and Centre of Mass

Centre of Gravity (CG): This is the theoretical point where the weight of an object is balanced, determining its stability and behavior under various forces. The CG is essential for understanding how objects behave when subjected to external forces, like gravity and motion, impacting their equilibrium.
Centre of Mass (CM): The CM is the point where the mass of an object is concentrated, significantly relevant in physics and engineering to analyze motion and balance. The CM is important in understanding how objects will respond to forces applied at different locations because it represents the average position of all mass in an object.
- CG and CM are often used interchangeably, but they differ in practical applications: CG is essential in analyzing weight distribution and stability, while CM is critical in understanding the dynamics of motion and inertia.

Free Body Diagrams

Step 1: Identify and isolate the free body under consideration, which involves defining the boundaries of the system you’re analyzing. This step is crucial for focusing on specific interactions without external distractions.
Step 2: Establish a coordinate reference frame to provide a context for describing motion or forces. This helps in visualizing the problem in a structured manner, enabling clearer analysis of forces and movements.
Step 3: Draw internal (muscular) and external forces acting on the system, clearly indicating the direction and points of application of these forces. Understanding these forces is essential for determining their impact on the body or object of study.
Step 4: Draw the joint reaction force, which illustrates how two bodies interact at their point of contact. This helps in visualizing how forces are transferred and absorbed, critical in understanding biomechanics and mechanical systems.
Step 5: Write the equations of motion governing the system based on the forces and interactions drawn. This step is crucial for solving problems related to dynamics and kinematics, allowing predictions of future movements and forces.

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Description

Explore the fundamental concepts of Newton's Laws of Motion, the impulse-momentum relationship, and the principles of work, power, and energy. This quiz will test your understanding of how forces affect motion and the interplay between impulse and momentum. Perfect for students studying introductory physics!