 # Physics I

This collection covers classical mechanics and thermodynamics discussing relevant laws and equations; every topic is presented with experiments validating theoretical hypothesis, and real world contextual examples.

• Newton's Laws of Motion

Source: Andrew Duffy, PhD, Department of Physics, Boston University, Boston, MA

This experiment examines at various situations involving two interacting objects.

First, the experiment examines the forces that two objects apply to one another while they collide. The objects are wheeled carts that have variable masses. The purpose of this experiment is to discover when the force the first cart exerts on the other is the same magnitude as the force the second cart exerts back on the first, as well as when these two forces have different magnitudes. Second, it examines the forces that two objects exert on one another when one cart is pushing or pulling the second one. Again, the focus is on exploring the situations in which the two forces have the same magnitude and in which they have different magnitudes.

• Force and Acceleration

Source: Nicholas Timmons, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

The goal of this experiment is to understand the components of force and their relation to motion through the use of Newton's second law by measuring the acceleration of a glider being acted upon by a force.

Nearly every aspect of motion in everyday life can be described using Isaac Newton's three laws of motion. They describe how objects in motion will tend to stay in motion (the first law), objects will accelerate when acted upon by a net force (the second law), and every force exerted by an object will have an equal and opposite force exerted back onto that object (the third law). Almost all of high school and undergraduate mechanics is based on these simple concepts.

• Vectors in Multiple Directions

Source: Nicholas Timmons, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

This experiment demonstrates how vectors add and subtract in multiple directions. The goal will be to analytically calculate the addition or subtraction of multiple vectors and then to experimentally confirm the calculations.

A vector is an object with both magnitude and direction. The magnitude of a vector is simply denoted as the length, while the direction is typically defined by the angle it makes with the x-axis. Because forces are vectors, they can be used as a physical representation of vectors. By setting up a system of forces and finding which additional force will create an equilibrium between the forces, a system of vectors can be experimentally verified.

• Kinematics and Projectile Motion

Source: Ketron Mitchell-Wynne, PhD, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

This experiment demonstrates the kinematics of motion in 1 and 2 dimensions. This lab will begin by studying motion in 1 dimension, under constant acceleration, by launching a projectile directly upward and measuring the maximum height reached. This lab will verify that the maximum height reached is consistent with the kinematic equations derived below. Motion in 2 dimensions will be demonstrated by launching the ball at an angle θ. Using the kinematic equations below, one can predict the distance to where the projectile will land based upon the initial speed, total time, and angle of trajectory. This will demonstrate kinematic motion with and with out acceleration in the y- and x-directions, respectively.

• Newton's Law of Universal Gravitation

Source: Ketron Mitchell-Wynne, PhD, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

Legend states that Isaac Newton saw an apple fall from a tree. He noticed the acceleration of the apple and deduced that there must have been a force acting upon the apple. He then surmised that if gravity can act at the top of the tree, it can also act at even larger distances. He observed the motion of the moon and the orbits of the planets and eventually formulated the universal law of gravitation. The law states that every particle in the universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them. This force acts along the line joining the two particles. Gravitational acceleration g, which is the acceleration an object on the surface of the Earth experiences due to the Earth's gravitational force, will be measured in this lab. Accurately knowing this value is extremely important, as it describes the magnitude of the gravitational force on an object at the surface of the Earth.

• Conservation of Momentum

Source: Nicholas Timmons, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

The goal of this experiment is to test the concept of the conservation of momentum. By setting up a surface with very little friction, collisions between moving objects can be studied, including their initial and final momenta.

The conservation of momentum is one of the most important laws in physics. When something is conserved in physics, the initial value is equal to the final value. For momentum, this means that the total initial momentum of a system will be equal to the total final momentum. Newton's second law states that the force on an object will be equal to the change in the object's momentum with time. This fact, combined with the idea that momentum is conserved, underpins the workings of classical mechanics and is a powerful problem-solving tool.

• Friction

Source: Nicholas Timmons, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

The goal of this experiment is to examine the physical nature of the two types of friction (i.e., static and kinetic). The procedure will include measuring the coefficients of friction for objects sliding horizontally as well as down an inclined plane.

Friction is not completely understood, but it is experimentally determined to be proportional to the normal force exerted on an object. If a microscope zooms in on two surfaces that are in contact, it would reveal that their surfaces are very rough on a small scale. This prevents the surfaces from easily sliding past one another. Combining the effect of rough surfaces with the electric forces between the atoms in the materials may account for the frictional force. There are two types of friction. Static friction is present when an object is not moving and some force is required to get that object in motion. Kinetic friction is present when an object is already moving but slows down due to the friction between the sliding surfaces.

• Hooke's Law and Simple Harmonic Motion

Source: Ketron Mitchell-Wynne, PhD, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

Potential energy is an important concept in physics. Potential energy is the energy associated with forces that depend upon the position of an object relative to its surroundings. Gravitational potential energy, which is discussed in another video, is the energy associated that is directly proportional to the height of an object above the ground. Similarly, it is possible to define spring potential energy, which is directly proportional to the displacement of a spring from its relaxed state. A stretched or compressed spring has potential energy, as it has the ability to do work upon an object. The “ability to do work” is often quoted as the fundamental definition of energy. This video will demonstrate the potential energy stored in springs. It will also verify the restoring force equation of springs, or Hooke’s Law. The spring constant is different for springs of different elasticities. Hooke’s law will be verified and the spring constant measured by attaching varying weights to a suspended spring and measuring the resulting displacements.

• Equilibrium and Free-body Diagrams

Source: Ketron Mitchell-Wynne, PhD, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

Equilibrium is a special case in mechanics that is very important in everyday life. It occurs when the net force and the net torque on an object or system are both zero. This means that both the linear and angular accelerations are zero. Thus, the object is at rest, or its center of mass is moving at a constant velocity. However, this does not mean that no forces are acting on the objects within the system. In fact, there are very few scenarios on Earth in which no forces are acting upon any given object. If a person walks across a bridge, they exert a downward force on the bridge proportional to their mass, and the bridge exerts an equal and opposite upward force on the person. In some cases, the bridge may flex in response to the downward force of the person, and in extreme cases, when the forces are great enough, the bridge may become seriously deformed or may even fracture. The study of this flexing of objects in equilibrium is called elasticity and becomes extremely important when engineers are designing buildings and structures that we use every day.

• Torque

Source: Nicholas Timmons, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

The goal of this experiment is to understand the components of torque and to balance multiple torques in a system to achieve equilibrium. Much like how a force causes linear acceleration, torque is a force that causes a rotational acceleration. It is defined as the product of a force and the distance of the force from the axis of rotation. If the sum of the torques on a system is equal to zero, the system will not have any angular acceleration.

• Rotational Inertia

Source: Nicholas Timmons, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

Inertia is the resistance of an object to being accelerated. In linear kinematics, this concept is directly related to the mass of an object. The more massive an object, the more force is required to accelerate that object. This is seen directly in Newton's second law, which states that force is equal to mass times acceleration. For rotation, there is a similar concept called rotational inertia. In this case, rotational inertia is the resistance of an object to being rotationally accelerated. Rotational inertia is dependent not only upon mass, but also upon the distance of mass from the center of rotation. The goal of this experiment is to measure the rotational inertia of two rotating masses and to determine the dependence upon mass and distance from the axis of rotation.

• Angular Momentum

Source: Nicholas Timmons, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

Angular momentum is defined as the product of the moment of inertia and the angular velocity of the object. Like its linear analog, angular momentum is conserved, meaning that the total angular momentum of a system will not change if there are no external torques on the system. A torque is the rotational equivalent of a force. Because it is a conserved, angular momentum is an important quantity in physics. The goal of this experiment is to measure the angular momentum of a rotating rod and to use the conservation of angular momentum to explain two rotational demonstrations.

• Energy and Work

Source: Ketron Mitchell-Wynne, PhD, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

This experiment demonstrates the work-energy principle. Energy is one of the most important concepts in science and is not simple to define. This experiment will deal with two different kinds of energy: gravitational potential energy and translational kinetic energy. Gravitational potential energy is defined as the energy an object possesses because of its placement in a gravitational field. Objects that are high above the ground are said to have large gravitational potential energy. An object that is in motion from one location to another has translational kinetic energy. The most crucial aspect of energy is that the sum of all types of energy is conserved. In other words, the total energy of a system before and after any event may be transferred to different kinds of energy, wholly or partly, but the total energy will be the same before and after the event. This lab will demonstrate this conservation. Energy can be defined as "the ability to do work," which relates mechanical energy with work. Flying projectiles that hit stationary objects do work on those stationary objects, such as a cannonball hitting a brick wall and breaking it apart or a hammer driving a nail in to a piece of wood. In all cases, there is a force exe

• Enthalpy

Source: Ketron Mitchell-Wynne, PhD, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

When a pot of water is placed on a hot stove, heat is said to "flow" from the stove to the water. When two or more objects are placed into thermal contact with each other, heat spontaneously flows from the hotter objects to the colder ones, or in the direction that tends to equalize the temperature between the objects. For example, when ice cubes are put in a cup of room-temperature water, heat from the water flows to the ice cubes and they begin to melt. Often, the term "heat" is used inconsistently, usually to simply refer to the temperature of something. In the context of thermodynamics, heat, like work, is defined as a transfer of energy. Heat is energy transferred from one object to another because of a difference in temperature. Furthermore, the total energy of any isolated thermodynamic system is constant-that is, energy can be transferred to and from different objects within the system and can be transformed to different types of energy, but energy cannot be created or destroyed. This is the first law of thermodynamics. It is very similar to the conservation of energy law discussed in another video, but in the context of heat and thermodynamic processes. In the case of ice cubes in water, if the first law of thermodyn

• Entropy

Source: Ketron Mitchell-Wynne, PhD, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

The second law of thermodynamics is a fundamental law of nature. It states that the entropy of a system always increases over time or remains constant in ideal cases when a system is in a steady state or undergoing a "reversible process." If the system is undergoing an irreversible process, the entropy of the system will always increase. This means that the change in entropy, ΔS, is always greater than or equal to zero. The entropy of a system is a measure of the number of microscopic configurations the system can attain. For example, gas in a container with known volume, pressure, and temperature can have an enormous number of possible configurations of the individual gas molecules. If the container is opened, the gas molecules escape and the number of configurations increases dramatically, essentially approaching infinity. When the container is opened, the entropy is said to increase. Therefore, entropy can be considered a measure of the "disorder" of a system.