Studied by 15 peopleConvection
Definition: is the transfer of heat through the movement of fluids (liquids or gases). This movement creates a transfer of heat from one part of the fluid to another, carrying heat along with the moving fluid.
Example: Boiling water in a pot where the hot water rises to the top, and cooler water moves down, creating a continuous circulation of heat.
Thermal Energy
refers to the internal energy of a system arising from the motion of its particles. It is associated with the temperature of the system, where higher temperatures typically indicate greater thermal energy. The motion of atoms and molecules within a substance contributes to its thermal energy, and this energy can be transferred between objects through processes like conduction, convection, and radiation. Thermal energy is a fundamental aspect of thermodynamics and plays a crucial role in understanding and describing heat-related phenomena.
Closed System
is a physical system that does not exchange matter with its surroundings, but energy can be exchanged with the surroundings. In other words, while energy (such as heat or work) can enter or leave the system, the total mass of the system remains constant. These systems are often conceptualized in physics, thermodynamics, and engineering analyses to simplify the consideration of energy transfers without the complication of mass exchange. An example: could be a sealed container where heat can be added or removed, but no matter enters or leaves the container during the process.
Isolated System
is a physical system that does not exchange either matter or energy with its surroundings. In other words, it is a closed system with the additional constraint that there is no transfer of energy (heat or work) between the system and its surroundings. These systems are theoretical constructs used in physics and thermodynamics to simplify analyses and focus on specific aspects, such as conservation of energy and mass. In practice, truly isolated systems are difficult to achieve, but the concept is valuable for theoretical considerations and understanding fundamental principles
Conductive Heat Loss
also known as thermal conduction, occurs when heat transfers through a material due to the direct contact and collision of particles within that material. In simpler terms, it is the process by which heat moves through a substance without any significant movement of the material itself. Materials that are good conductors allow heat to pass through them easily, while poor conductors (insulators) impede the flow of heat. This heat loss is commonly observed in scenarios where one end of a material is exposed to a higher temperature, causing the heat to travel through the material to the cooler end. Examples include the heat transfer through metal rods or the walls of a building
Conduction
Definition: the process of heat transfer through a material without any movement of the material itself. It occurs when vibrating particles transfer energy to neighboring particles in direct contact.
Example: Heating one end of a metal rod will cause the other end to become hot as heat is conducted through the metal.
Radiation
Definition: is the transfer of heat in the form of electromagnetic waves (such as light waves). Unlike conduction and convection, does not require a medium and can occur in a vacuum.
Example: The Sun radiates heat in the form of sunlight, which travels through space to reach and warm the Earth.
Photoelectric effect
a phenomenon in which light of sufficiently high frequency incident on a metal in a vacuum causes the metal to emit electrons
A gas system undergoes rapid compression followed by isothermal expansion. Which of the following statements correctly describes change in total internal energy?
a) Total internal energy increases
b) Total internal energy decreases
c) Total internal energy stays the same
d)More info needed to answer question
Answer: a) Total internal energy increases
explanation:
During the rapid compression, work is done on the system. This means that energy is transferred into the system and the internal energy increases. Because the compression happens rapidly, not all this energy is lost through heat. By definition, isothermal processes do not change internal energy. The total process, therefore, results in an increase in internal energy.
One classic example of a thermodynamically closed system is a vessel full of gas with a movable piston. Which of the following quantities must remain constant as the piston compresses the gas?
a) Moles of gas
b) The internal energy of the system
c) The enthalpy of the system
d) The Gibbs free energy of the system
Answer: Moles of gas
Explanation: Closed systems are capable of exchanging energy, but not matter, with the surroundings. Since matter can't enter or leave the system, this value will remain constant.
If the newton is the product of kilograms and meters/second?, what units comprise the pound?
Force will obey the same relationship with mass and acceleration, regardless of the unit system. Force is always the product of mass and acceleration, so one pound (Ib) must be equal to one slug . ft/ s^2
Order the following units from smallest to largest: centimeter, angstrom, inch, mile, foot.
angström < centimeter < inch < foot < mile
When calculating the sum of vectors A and B (A + B), we put the tail of B at the tip of A. What would be the effect of reversing this order?
Vector addition, unlike vector multiplication, is a commutative function.
The resultant of A + B is the same as B + A, so there would be no difference between the two resultants.
When calculating the difference of vectors A and B (A - B), we invert B and put the tail of this new vector at the tip of A. What would be the effect of reversing this order (B - A)?
Vector subtraction, like vector multiplication, is not a commutative function.
The resultant of A - B has the same magnitude as B - A, but is oriented in the opposite direction.
How is a scalar calculated from the product of two vectors? How is a vector calculated?
• Scalar: A scalar is calculated from two vectors by using the dot product:
A •B = |A| |B| cos (θ)
• Vector: A vector is calculated by using the cross product:
A × B = |A| |B| sin (θ)
True or False: If C = A x B, where A is directed toward the right side of the page
and B is directed to the top of the page, then C is directed midway between A and B at a 45° angle.
False. This would be true of an addition problem in which both vectors have equal magnitude, but it is never true for vector multiplication. To find the direction of C, we must use the right-hand rule. If the thumb points in the direction of A, and the fingers point in the direction of B, then our palm, C, points out of the page.
What is the relationship between instantaneous velocity and instantaneous speed? Between average velocity and average speed?
Instantaneous speed is the magnitude of the instantaneous velocity vector. Average speed and average velocity may be unrelated because speed does not depend on displacement, but is rather the total distance traveled divided by time.
True or False: Total distance traveled can never be less than the total displacement.
True. Displacement considers the most direct route between two points.
Distance will always be equal to or larger in magnitude than displacement.
Provide a definition for displacement or velocity in terms of the other variable.
Velocity is the rate of change of the displacement of an object. Displacement is a function of velocity acting over a period of time.
When calculating frictional forces, how is directionality assigned?
The direction of the frictional force always opposes movement. Once the instantaneous velocity vector is known (or net force, in the case of static friction), the frictional force must be in the opposite direction.
When no force is being applied, the velocity must be:
If there is no net force acting on an object, then that object is not experiencing an acceleration and it has a constant velocity.
True or False: The Earth creates a larger force on you than you create on the Earth.
False. Forces are always reciprocal in nature. When the Earth exerts a force on a person, the person also exerts a force of the same magnitude on the Earth (in the opposite direction). The difference in masses gives the Earth an apparent acceleration of zero.
Name two forces in addition to mechanical manipulation (pushing or pulling forces created by contact with an object)
Gravity and frictional forces were discussed in this chapter. Electrostatic, magnetic, elastic, weak nuclear, and strong nuclear forces are other examples of forces.
In your own words, provide a description of Newton's laws of motion:
1. In the absence of any forces—or when the net force is zero-there will be no change in velocity.
Acceleration results from the sum of the force vectors
For any two interacting objects, all forces acting on one object have an equal and opposing force acting on the other object
During a test crash, a 500 kg car is driven at a constant velocity of 50 mph until it hits a wall without braking. Apply all three of Newton's laws to this situation.
Prior to the collision, the vehicle is travelling at constant velocity, which (according to Newton's first law) indicates that there is no acceleration and no net force.
The collision with the wall creates a sudden deceleration. Because there is acceleration, there must be a net force. The value of the net force can be calculated by multiplying the mass of the car times the acceleration.
When the car collides with the wall, the car exerts a force on the wall. Simul-taneously, the wall exerts a force of equal magnitude in the opposite direction on the car.
How do the forces acting in free fall and projectile motion differ?
The only force acting in both free fall and projectile motion is gravity.
At what angle of launch is a projectile going to have the greatest horizontal displacement? What angle will result in the greatest vertical displacement, assuming a level surface?
• Greatest horizontal displacement: The product of sine and cosine is maximized when the angle is 45°. Because horizontal displacement relies on both measurements, the maximum horizontal displacement will also be achieved at this angle.
• Greatest vertical displacement: Vertical displacement will always be zero as the object returns to the starting point. Objects launched vertically will experience the greatest vertical distance.
What is the equation for centripetal acceleration?
If the equation for centripetal force is Fc = mv^2/r and force is simply mass times acceleration (from Newton's second law), then ac = v^2/r
Can a moving object be in equilibrium? Why or why not?
A moving object can be in either translational or rotational equilibrium (or both). Translational equilibrium only requires the net force on an object be zero-its velocity is constant. The corresponding condition in rotational equilibrium is that net torque equals zero-its angular velocity is constant.
If you have an object three times as heavy as you can lift, how could a lever be used to lift the object? Where would the fulcrum need to be placed?
One could place the fulcrum one quarter of the way across the lever, closer to the object. The ratio of the lever arms would then be 3:1, which means that only one-third of the original force is necessary. (Alternatively, the fulcrum could be placed at the end with the object one-third of the way across the lever. This would again result in a 3:1 ratio of lever arms, meaning that only one-third of the original force is necessary.)
Define kinetic energy and potential energy.
• Kinetic energy: Kinetic energy is the energy of motion. It is related to the mass of an object, as well as its speed squared.
• Potential energy: Potential energy is energy associated with a given position or intrinsic property of a system; it is stored in gravitational, electrical, elastic, or chemical forms.
Gravitational potential energy is directly related to the mass of the object and its height above a reference point.
Compare and contrast conservative and nonconservative forces:
What happens to total mechanical energy of the system?
Conservative: Remains constant
nonconservative: decreases (energy is dissipated)
Does the path taken matter?
Conservative: No
nonconservative: yes; more energy is dissipated with a longer path
What are some examples?
Conservative: Gravity, electrostatic forces, elastic forces (approximately conservative)
nonconservative: Friction, air resistance, Viscous drag
What are the units for work? How are work and energy different?
The unit of work is the joule, which is also the unit for energy. Work and energy are related concepts. By performing work, the energy of a system is changed.
Work, along with heat, is a form of energy transfer.
Provide three methods for calculating the work done on or by a system.
W = Fd cos (θ) (the dot product of the force and displacement vectors)
W = PΔV (the area under a pressure -volume curve)
Wnet = ΔK (the work - energy theorem)
While driving a vehicle at constant velocity on a flat surface, the accelerator must be slightly depressed to overcome resistive forces. How does the amount of work done by the engine (via the accelerator) compare to the amount of work done by resistance?
Begin by thinking about how each form of work is affecting the vehicle. While we could try to work through what may be happening in terms of forces and displacements, this gets very tricky when considering moving engine parts. In this case, it is simpler to think about each work in terms of kinetic energy. The work done by the engine increases the kinetic energy of the car, so it's positive.
Conversely, the work done by resistance decreases the kinetic energy of the car, meaning the work done on the car is negative. If the engine does more work than friction, then there is a positive change in kinetic energy. If resistance does more work, then the change is negative. If they do equal amounts of work, then there is no change in kinetic energy. We are given that the vehicle maintains a constant velocity; thus, there is no change in kinetic energy. Therefore, according to the work-energy theorem, the net work must also be zero, and we can infer that the amount of positive work done by the engine must be equal to the amount of negative work done by resistance.
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