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Questions and Answers
What is the equation that describes final velocity when initial velocity, acceleration, and time are known?
What is the equation that describes final velocity when initial velocity, acceleration, and time are known?
Which statement best describes Newton's First Law of Motion?
Which statement best describes Newton's First Law of Motion?
What is the unit of force defined by the equation F = ma?
What is the unit of force defined by the equation F = ma?
In the formula Weff = m(g + a), what does Weff represent?
In the formula Weff = m(g + a), what does Weff represent?
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Which of the following equations can be rearranged to find displacement when final and initial velocities are known?
Which of the following equations can be rearranged to find displacement when final and initial velocities are known?
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How does inertia relate to mass according to Newton's laws?
How does inertia relate to mass according to Newton's laws?
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When an object is in free fall, which of the following is usually the acceleration value taken for gravity?
When an object is in free fall, which of the following is usually the acceleration value taken for gravity?
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What happens to an object's weight when additional upward acceleration is applied?
What happens to an object's weight when additional upward acceleration is applied?
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What is the formula for calculating potential energy?
What is the formula for calculating potential energy?
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Which of the following describes the relationship between work and energy?
Which of the following describes the relationship between work and energy?
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What does the Work-Energy Principle state?
What does the Work-Energy Principle state?
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How do fighter pilots experience fewer effects from g-forces than most other individuals?
How do fighter pilots experience fewer effects from g-forces than most other individuals?
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What type of energy is associated with an object due to its position?
What type of energy is associated with an object due to its position?
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Which scenario illustrates the concept of conservation of energy?
Which scenario illustrates the concept of conservation of energy?
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What can result from rapid changes in acceleration, such as during ejection from a fighter jet?
What can result from rapid changes in acceleration, such as during ejection from a fighter jet?
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Which of the following statements about washing machines is true regarding g-forces?
Which of the following statements about washing machines is true regarding g-forces?
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What is the definition of acceleration?
What is the definition of acceleration?
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Which statement correctly differentiates between mass and inertia?
Which statement correctly differentiates between mass and inertia?
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What defines a vector quantity?
What defines a vector quantity?
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What is the work-energy principle?
What is the work-energy principle?
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According to Newton's laws, what happens when a net external force acts on an object?
According to Newton's laws, what happens when a net external force acts on an object?
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Which of the following statements about displacement is true?
Which of the following statements about displacement is true?
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What unit is used to measure velocity?
What unit is used to measure velocity?
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What is the significance of the acceleration due to gravity (g)?
What is the significance of the acceleration due to gravity (g)?
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What type of injury is primarily associated with bullets traveling at subsonic speeds?
What type of injury is primarily associated with bullets traveling at subsonic speeds?
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Which of the following factors influences the extent of injury caused by a bullet?
Which of the following factors influences the extent of injury caused by a bullet?
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Which phenomenon can cause injury even without direct contact from a bullet?
Which phenomenon can cause injury even without direct contact from a bullet?
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At what velocity is a bullet classified as supersonic?
At what velocity is a bullet classified as supersonic?
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What is the term used to describe the short-lived cavity formed during a bullet's passage?
What is the term used to describe the short-lived cavity formed during a bullet's passage?
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What effect do shock waves have on solid tissues like the liver and brain?
What effect do shock waves have on solid tissues like the liver and brain?
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What happens to liquids within the body when shock waves are applied?
What happens to liquids within the body when shock waves are applied?
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Which of the following best characterizes the relationship between bullet velocity and the type of injuries sustained?
Which of the following best characterizes the relationship between bullet velocity and the type of injuries sustained?
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What effect does bullet precession have on the bullet's trajectory?
What effect does bullet precession have on the bullet's trajectory?
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Which of the following statements best describes the impact of yawing on bullet performance?
Which of the following statements best describes the impact of yawing on bullet performance?
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What is the primary purpose of a Full Metal Jacket on a bullet?
What is the primary purpose of a Full Metal Jacket on a bullet?
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How does an unstable bullet affect wound characteristics?
How does an unstable bullet affect wound characteristics?
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What is the consequence of high velocity in rifle bullets when striking a target?
What is the consequence of high velocity in rifle bullets when striking a target?
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What phenomenon can cause secondary injuries when a bullet impacts a target?
What phenomenon can cause secondary injuries when a bullet impacts a target?
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Which of the following factors does NOT significantly influence the bullet's wound path?
Which of the following factors does NOT significantly influence the bullet's wound path?
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What role does friction play in a bullet's journey down the barrel?
What role does friction play in a bullet's journey down the barrel?
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What is the main factor influencing the severity of a gunshot wound?
What is the main factor influencing the severity of a gunshot wound?
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Which of the following correctly describes bullet design factors?
Which of the following correctly describes bullet design factors?
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What phenomenon involves the temporary cavity created in tissue due to bullet penetration?
What phenomenon involves the temporary cavity created in tissue due to bullet penetration?
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How does doubling the bullet velocity affect kinetic energy?
How does doubling the bullet velocity affect kinetic energy?
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What kind of injury is primarily caused by the shock waves from a gunshot?
What kind of injury is primarily caused by the shock waves from a gunshot?
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Which type of firearm generally has more kinetic energy due to higher pressure and propellant?
Which type of firearm generally has more kinetic energy due to higher pressure and propellant?
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What happens to the energy transferred during a gunshot wound when the bullet mass is doubled?
What happens to the energy transferred during a gunshot wound when the bullet mass is doubled?
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Which aspect differentiates pistols from revolvers in terms of bullet mechanisms?
Which aspect differentiates pistols from revolvers in terms of bullet mechanisms?
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Study Notes
G-Force and Fighter Pilots
- Fighter pilots routinely experience 9g accelerations during combat maneuvers.
- Group Captain Sir Douglas Bader lost both legs in a crash in 1931.
- He was credited with 20 aerial victories in WWII.
- Bader recovered more quickly from g-force induced blackouts than other pilots.
- He had no legs for the blood to pool into during high g maneuvers.
- Ejection seats create up to 25g, often resulting in spinal injury even when executed correctly.
- Washing machines can create up to 200g during the spin cycle, fatal for toddlers.
- Peregrine falcons can dive at prey at speeds exceeding 320 kph, experiencing over 20g when pulling out of their dives.
Effective Weight
- Effective weight can be less than gravitational weight under certain conditions.
- The difference in weight is related to the force acting on the object.
Why We Feel Faint
- Getting up quickly from a reclining position, especially after sleeping, can cause faintness.
- Upwards acceleration causes blood to have a higher effective weight, making it harder for the heart to pump blood to the brain.
Work and Energy
- Work is done when a force moves a body through a distance along the direction of the force.
- Work is measured in Joules (J).
- Energy is the capacity or ability to do work.
- Energy is also measured in Joules (J).
- 1J is the energy needed to exert a force of 1N over a distance of 1m.
Types of Energy
- Chemical energy
- Thermal energy
- Nuclear/atomic energy
- Acoustic energy
- Mechanical energy
Mechanical Energy
- Mechanical energy has two forms:
- Kinetic energy (resulting from movement)
- Potential energy (resulting from electrical charge, internal stress, or relative position)
Potential energy (PE)
- PE is calculated as PE = mgh (where h is the height above a reference point).
- PE can be converted to kinetic energy (KE).
Conservation of Energy
- Energy cannot be created or destroyed, only transformed from one form to another. This is known as the conservation of energy.
- The Work-Energy Principle states that the work done on an object is equal to the change in its kinetic energy.
Straight-Line Motion
- Straight-line motion can be described using Newton's Three Laws of Rectilinear Motion.
- These laws involve:
- Initial velocity (u)
- Final velocity (v)
- Displacement (s)
- Acceleration (a)
- Time (t)
Newton's Laws of Rectilinear Motion
- v = u + at
- v^2 = u^2 + 2as
- s = ut + ½at^2
Physics Professor Falling
- A physics professor falls 15m from a ladder.
- To calculate the impact velocity and duration of the fall, we need to understand what is known and unknown.
- Known:
- Initial velocity (u) = 0 ms-1
- Acceleration (a) = g = 9.81 ms-2 (approximated to 10 ms-2)
- Displacement (s) = 15m.
- Unknown:
- Final velocity (v)
- Time (t)
Impact Velocity
- Use an equation that includes v and only one unknown variable.
- The equation v = u + 2as can be used.
- The calculated velocity is approximately 62 kph, which is roughly equivalent to 40 mph.
Duration of Fall
- Use an equation that includes t and only one unknown variable.
- The equation s = ut + ½at^2 can be used.
- The duration of the fall can be calculated.
Forces
- Newton's First Law: "All objects tend to remain at rest or in uniform straight line motion (at constant velocity) unless acted upon by an external force.”
Changing Velocity
- An object will only change velocity (magnitude or direction) if and only if a force is exerted upon it.
Types of Forces
- Gravitational forces
- Electrostatic (Coulombic) forces
- Many other types of forces exist.
Newton's Second Law
- F = ma
- Force is defined as any action that alters, or tries to alter, a body's state of rest or uniform motion in a straight line.
- Force is measured in Newtons (N).
- 1N is the force that provides a 1kg mass with an acceleration of 1ms-2.
- Inertia refers to the tendency of an object to resist changes in its motion.
- Inertia has the same units as mass (kg).
- The greater the mass, the greater the resistance to change.
Weight
- Weight (W) is the most familiar force.
- W = mg (where g is the acceleration due to gravity).
- Effective weight (Weff) can be increased by applying additional forces.
- This increases the effective weight, seen when ascending in an elevator.
- Weff = m(g + a)
Effective Weight Explained
- Effective weight changes when external forces act on a body.
- Weight is defined as a reaction force (opposite to the acceleration due to gravity) directed perpendicularly upwards from the surface.
Medical Applications of Physics (MAP)
- MAP.01.01: Define: time, displacement and distance, velocity and speed, acceleration.
- MAP.01.02: Differentiate between vectors and scalars.
- MAP.01.03: Explain Newton's Laws of Straight-Line Motion.
- MAP.01.04: Differentiate between mass, inertia and momentum.
- MAP.01.05: Describe the role of external forces in effective weight and g-force.
- MAP.01.06: Define work, power and energy.
- MAP.01.07: Differentiate between kinetic energy and potential energy.
- MAP.01.08: Differentiate between the conservation of energy and the Work-Energy Principle.
Concepts in Mechanics
- Time (t): The indefinite continued progress of existence and events. Units: seconds (s)
- Displacement (s): Distance measured in a given direction. Units: meters (m). This is a vector quantity.
- Distance: A scalar quantity.
- Velocity (v): Rate of change of displacement. Displacement is a vector quantity. Units: meters per second (ms-1).
- Acceleration (a): Rate of change of velocity. Units: meters per second per second (ms-2).
- Deceleration: Occurs when the velocity reduces and the acceleration value is negative.
- Acceleration due to gravity (g): 9.81ms-2. This is a constant, and objects of different masses fall at the same rate.
Units: The Meter (m)
- Originally defined as one ten-millionth of the distance from the Earth's equator to the North Pole.
- Since 1983, defined as the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second.
- Speed of light in a vacuum = 299,792,458 m/s
- Earth's polar circumference = 40,007 km
- Earth's equatorial circumference = 40,075 km
Gunshot Injuries
- The severity of gunshot wounds (GSWs) is determined by the amount of kinetic energy transferred from the bullet to the victim.
- Kinetic Energy (KE) = ½mv2
- Kinetic energy is increased by increasing either bullet mass or bullet velocity.
Factors Influencing Gunshot Wound Severity
- Rifle or Handgun: Rifles typically have larger cartridges and thicker barrels to withstand high pressures, resulting in greater kinetic energy transfer.
- Handgun Type: Pistols often have lower muzzle velocities than revolvers due to smaller cartridges required by their design.
- Bullet Design: Hollowpoint or expanding bullets deform on impact, increasing their kinetic energy transfer and causing more serious injuries.
Bullet Stability and Trajectory
- Bullet stability in flight affects accuracy, the size of the entrance wound, and the amount of damage caused along the wound path.
- All bullets are aerodynamically unstable, but some are more unstable than others.
- Yaw: Periodic movement along the longitudinal axis of a projectile.
- Tumbling: A complete 90° turn of the bullet beyond yawing.
- Spin: Provides gyroscopic stability which counteracts yawing and maintains the bullet's nose-on orientation.
- Precession: Complex spiral movement of the bullet's nose caused by spin.
- Nutation: Oscillation of the bullet's longitudinal axis.
- Bullet precession reduces with distance from the weapon.
- Yaw, nutation, and precession all contribute to the bullet rarely presenting minimum surface area at the point of impact, thus contributing to wound severity.
Bullet Composition and Jacket Separation
- Friction caused by the bullet traveling down the barrel can melt lead.
- Rifle bullets are usually covered with a metal jacket (copper or nickel), referred to as a "Full Metal Jacket", to prevent lead melting. The jacket is often separated from the bullet on impact, creating secondary wound tracks.
Bullet Velocity and Wound Severity
- Subsonic Velocity (below 340 ms-1): Laceration and crushing injuries are common, with damage primarily limited to direct bullet contact.
-
Supersonic Velocity (above 340 ms-1): More serious, indirect injuries can occur due to
- Shock Wave: A wave of pressure that can cause injury even without direct contact with the projectile. It is more damaging to solid tissues and enclosed liquids.
- Temporary Cavitation: A short-lived, expanding cavity formed by the bullet's passage.
- Permanent Cavity: The final wound track left by the bullet.
The Hydraulic Effect
- Shock wave injury can be particularly severe to enclosed liquids within the body, such as the bladder, heart, bowels, and eyes, because liquids are incompressible.
- This is known as the hydraulic effect, following Pascal's principle.
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Description
Explore the exhilarating world of g-forces experienced by fighter pilots and the science behind effective weight and faintness. Discover unique cases like Group Captain Sir Douglas Bader and learn about the incredible forces at play during aerial maneuvers and everyday machines. Understand how these concepts apply to both humans and nature.
