PHYSICS 221 Topic Checklist
UNIT 2
At the end of each chapter, be sure that you are familiar with all the listed topics and can do the homework problems associated with them.
Chapter 6 Work and Energy This along with chapters two and four form the core of the science of physics. There are few areas of any science or technology in which motion, force and energy do not play an important role.
q Work Work is done when a force acts on a moving object. It is defined as the product of the parallel component of the force multiplied by the displacement.
The MKS unit of work is Nm = kg m2/s2 = Joule (J).
q Energy A simple way of thinking about energy is to say it is a property of an object that gives it the ability to perform work. There are many kinds of energy because there are many different properties, such as motion, temperature, and elevation to name just a few, that a body may possess which might enable it to do work.
q Kinetic Energy This is the form of energy that a moving body possesses.
The MKS unit of energy is the same as the unit of work, the Joule.
q The Work - Energy Theorem During any given displacement the total amount of work done to a body is equal to the change of that object’s kinetic energy.
§ If the net work is positive the body will speed up.
§ If the net work is negative the body will slow down.
§ If the net work is zero the body will undergo no change of speed.
q Potential Energy This is the form of energy that a body possesses because of its position relative to another body. Examples are the gravitational energy of masses and the electrical energy of charges.
q Gravitational Potential Energy Gravitational energy is determined by the difference in elevation between an object and a reference level.
Only the change of potential energy is meaningful in a problem.
q Conservation of Energy A force is said to be conservative if the work it does depends on the initial and final positions but not on the actual path followed between these points. Examples are the gravitational and elastic types of forces. Gravity does the same amount of work on you when you go from the first floor to the third whether you walk up the stairs or take the elevator. The work done by nonconservative forces does depend on the path. The most common nonconservative force is friction. The total work done by all nonconservative forces is equal to the change of kinetic energy plus change of potential energy.
Energy may be transformed from one type to another or transferred from one body to another but it may never be created or destroyed.
q Power is the rate at which work is done. Since doing work always involves the transformation of energy we may also call power the rate at which energy is transformed.
The unit of power is J/s = watt (W). The power developed by a force acting on a body moving at constant speed is:
Chapter 7 Momentum In addition to kinetic energy, moving bodies also possess momentum. Momentum has properties that make it useful in solving problems involving collisions, recoils and other situations characterized by brief sudden forces.
q Momentum The linear momentum of an object is defined as the product of its mass and velocity:
The unit of momentum is kg m/s. There is no special name.
q Momentum and Force The net force acting on a body equals its rate of change of momentum.
q Conservation of Momentum No matter what happens inside an isolated system, the total momentum of the system remains constant: momentum before = momentum after
q Elastic and Inelastic Collisions
§ Elastic: No kinetic energy is lost during the impact.
§ Inelastic: The objects stick together after the impact.
Chapter 8 Rotation This chapter deals with the special properties of spinning bodies.
q Radian Measure Learn to use radians as well as degrees to measure angles.
q Conversion between Degrees and Radians
q Angular Velocity The rate at which an object is spinning.
The unit of angular velocity is rad/s. 1 rpm = 0.1047 rad/s
q Angular Acceleration The rate at which angular velocity is changing.
The unit of angular acceleration is rad/s2.
q Relation Between Angular and Linear Quantities
q Uniform Angular Acceleration The equations for constant angular acceleration are similar to those for constant linear acceleration (see chap 2). Just replace x with q, v with w, and a with a.
q Torque This is the twisting effect of a force. It is the product of the force times its lever arm.
q Moment of Inertia This is a body’s opposition to being rotated about an axis.
To find the moments of inertia of several common shapes, refer to the table of formulas in the book.
q Rotational Dynamics The effect of an applied torque is to cause angular acceleration.
q Rotational Kinetic Energy
q Angular Momentum
The angular momentum of a rotating body remains constant if the applied torque is zero. This allows skaters and other athletes to control their angular speed.
Chapter 9 Equilibrium, Strength of Materials This chapter provides an important application of the laws of force. It deals with the problem of designing and constructing structures that are strong enough to be stable and safe.
q Conditions for Equilibrium An object will be in equilibrium if the resultant of all forces and torques acting on it are zero.
q Problem Solving Be able to calculate the internal forces in a structure. ALWAYS START WITH A FORCE DIAGRAM.
q Elasticity Real objects change shape under the application of force. The applied force provides the stress and the resulting deformation is the strain.
q Elastic Modulus
q Bulk Modulus
q Fracture Know how to use tables of tensile and compressive strength to determine if a structure is strong enough to support a given load.
Chapter 10 Fluids The term fluid refers to substances that can flow. Liquids and gasses are both fluids.
q Density Density is mass per unit volume.
The MKS unit of density is kg/m3. Other units are g/cm3 and lb/ft3. Note that the last unit is actually weight density not mass density.
q Specific Gravity This is a dimensionless way of stating density. It is the density of an object divided by the density of water.
q Pressure Pressure is force per unit area.
The MKS unit is N/m2 = Pascal (Pa). Many other units are also in common use.
q Liquid Pressure The pressure at depth h in a liquid of density r is:
q Atmospheric Pressure The force exerted by the weight of the atmosphere on 1 m2 of surface. 1 atm = 1.013 x 105 N/m2 .
q Gauge Pressure The difference between absolute pressure and atmospheric pressure is called gauge pressure.
q Pressure Gauges Know the principles of operation of the barometer and manometer.
q Pascal’s Principle Any pressure applied to a confined liquid is transmitted undiminished to all points of the liquid.
q Buoyancy Archimedes’ Principle states that the buoyant force on a body immersed in a fluid is equal to the weight of the fluid displaced by that object. Be able to apply this idea to the cases of apparent weight of submerged objects, flotation, and density measurement. Here are some general observations about buoyancy:
§ For all bodies, the difference between the “true” mass and the “apparent” mass is the mass of displaced fluid. Note that these quantities are frequently called “true weight” and “apparent weight”.
§ For floating bodies, the mass of the body equals the mass of fluid displaced.
§ For completely submerged bodies, the volume of the body equals the volume of fluid displaced.