Work and Energy Notes (Etkina 6 & Knight 8.3 & 10) Flashcards
work is equivalent to changes in the system’s
energy
higher above Earth: greater
gravitational potential energy
faster an object is moving: greater
kinetic energy
elastic potential energy is the energy associated with an elastic object’s
degree of stretch
greater stretch/compression: greater
elastic potential energy
energy associated with both temperature and structure is called
internal energy
when the external force is in the direction of the object’s displacement, the external force does …, causing the system to …
positive work; gain energy
if the external force points opposite a system object’s displacement, the external force does …, causing the system’s energy to …
negative work; decrease
in the external force points perpendicular to a system object’s displacement, the external force does … work on the system, causing … to its energy
zero; no change
work is a … physical quantity. F is always …, distance (d) is always …. Only … can negate the value for work
scalar; positive; positive; the angle
if there is no work done on the system, the energy of the system should be
constant
energy is a … quantity: it is constant in an … system and changes as a result of … done on a … system
conserved; isolated; work; nonisolated
law of conservation of energy: the sum of the initial energies of a system plus the work done on the system by external forces equals the sum of the
final energies of the system
it is preferable to have a … system so that the changes occurring can be included as … within the system rather than as the … done by external forces
larger; energy changes; work
the gravitational potential energy of an object-Earth system is Ug =
mgy
y is the position of the object with respect to the … of a … coordinate system
zero; vertical
if earth is not included in the system, earth would be an … doing … on the system. The choice of system, though, … affect the result of analysis
external object; positive work; does not
when you stretch or compress an elastic spring-like object, you have to pull or push harder the more the object is stretched or compressed. the force is not …
constant
the coefficient of proportionality, k, in the equation F= kx, is called the ….
spring constant
… springs have larger values of k
stiffer
for k = 1 N/m, to stretch a spring by 1.0 m we would have to exert a
1.0 N force
Hooke’s law: if any object causes a spring to stretch/compress, the spring exerts an … on that object. The spring constant k is measured in N/m and is a measure of the …. of the spring
X or l is the … that the object has been stretched/compressed
F =
elastic force; stiffness; distance; kx
elastic potential energy equation: Us =
1/2kx^2