Topic 11 - Work and Energy Flashcards
What is a system?
An object or group of objects.
What are the different ways energy can be stored in a system?
Kinetic store, gravitational potential store, chemical store, elastic potential store, nuclear store and internal store
What is a kinetic store?
The energy stored by an object’s movement.
What is a gravitational potential store?
The energy stored in objects raised above the Earth’s surface, due to the Earth’s gravitational field.
What is a chemical store?
The energy stored by the chemical bonds between atoms.
What is an elastic potential store?
The energy stored when an object is being stretched, compressed or squashed.
What is a nuclear store?
The energy stored in the nucleus of an atom that can be released by radioactive decay.
What is an internal store?
Sum of the kinetic energy stored in the particles of an object and the chemical energy stored in chemical bonds between particles in the object.
What is the equation for kinetic energy?
1/2 x mass x velocity2
What is the equation for the change in GPE?
Mass x gravitational field strength x change in height
What is energy measured in?
Joules
What is the equation for elastic potential energy?
1/2 x spring constant x extension2
What is the spring constant measured in?
N/m
What is the extension measured in?
Metres
What is the conservation of energy?
Energy cannot be created or destroyed, only transformed
How can energy be transformed?
Electrical work, heating, waves, mechanical work
What is electrical work?
When an electrical current transfers energy from one object to another.
How does heating transform energy?
Heating an object increases its internal energy.
How do waves transform energy?
Light and other types of waves can transfer energy from one object to another.
What is mechanical work?
When energy transferred from one object to another via a force.
What is the equation for work done?
Force x distance (moved along the line of action of the force)
How can more work be done?
Applying the same force over a longer distance, apply a larger force for the same distance.
What is work?
Total change in energy of/energy transferred to an object.
What is on the x-axis of an extension-load graph?
The extension of the spring
What is on the y-axis of an extension-load graph?
The force acting on the spring
What is a limit of proportionality?
When an object will not return to its original length when the force is removed.
What is extension directly proportional to?
The force applied
What happens if a spring is over-stretched?
It will not return to its original length
What relationship do spring constant and spring stiffness have?
The higher the spring constant, the stiffer the spring.
What is Hooke’s Law?
Force = spring constant x extension
Which letter is used to represent extension?
e or x
Which letter is used to represent spring constant?
k
Investigating Hooke’s Law 1
First, measure the original length of the spring.
Investigating Hooke’s Law 2
Next, hang different masses on the spring and measure the length of the spring in each case.
Investigating Hooke’s Law 3
Adding masses to the spring increases the downwards force as each mass has weight.
Investigating Hooke’s Law 4
The extension of the spring equals the length with masses minus the original length.
Investigating Hooke’s Law 5
Plot a graph with extension of the spring on the x axis and force on the y axis.
How can the extension of the spring be worked out in an investigation?
Length of the loaded spring − natural length of the spring
What apparatus is needed to investigate Hooke’s Law?
A spring, a ruler and a known mass
What happens when a spring is compressed?
Elastic potential energy is stored in the spring (so long as a spring isn’t inelastically deformed).
What is the elastic potential energy stored in a stretched spring equal to?
The work done when stretching it
What does the area under a force-extension graph show?
The elastic potential energy stored in a stretched spring
What is the equation for percentage efficiency?
Useful energy output/total energy output x 100
How could the energy efficiency of a toy car be increased?
Improve aerodynamics and lubricate the track
Why does lubrication increase energy efficiency?
It reduces frictional forces, reducing dissipated energy
Why does aerodynamicising the car increase energy efficiency?
It reduces the effects of air resistance.
