Section 4 - Forces And Energy Flashcards
When a system changes, what happens to energy?
It is transferred
What is a system?
A single object or a group of objects that you’re interested in
When a system changes, what happens to some of the energy?
A small amount of energy is dissipated and stored in less useful ways
What are the three ways in which energy be transferred?
Heating
Doing work
Electrical equipment
How can energy be transferred by heating?
E.g. a pan of water is heated on a stove
When the system is the pan of water, energy is transferred into the system by heating to the thermal energy stores, which increases the temperature
When the system is the stove and the pan, energy is transferred from the chemical energy store of the gas to the thermal energy stores of the pan and the water
How is energy transferred by doing work?
E.g. a box being lifted off of the floor
The box is the system. As the box is lifted, work is done against gravity
This causes energy to be transferred to the box’s kinetic and gravitational potential energy stores
How is energy transferred by electrical equipment?
Electrical devices work by transferring energy between two different energy stores
E.g. electric ions transfer energy electrically from the mains power supply to the thermal energy store of their metal plates
If a force moves an object, what has been done?
Work
What is the equation for work done?
Force x distance moved in the direction of the force
What is work done?
When a force moves an object through a distance, work is done on the object and energy is transferred
What does Nm mean?
Newton metre
What is power?
How much work is done per second / rate of energy transfer
What is the equation for power?
Work done (J) / time taken (s)
The larger the power of an object, the more work it does per second
True or false?
True
A force doing work often causes a rise in what?
Temperature as energy is dissipated to the thermal energy stores of the moving object and its surroundings. This means that the process is wasteful and the efficiency of the process is reduced
Interactions between objects causes what?
Forces
Whenever two objects interact, both objects feel an equal but opposite force. What law is this?
Newton’s third law
What do free body force diagrams show?
All of the forces acting on an object
What is the resultant force?
The overall force on a point or object
Objects in equilibrium have a resultant force of what?
Zero. Objects in equilibrium are either stationary or moving at a steady speed (Newton’s first law)
How do you find resultant forces?
By using scale drawings
An object is in equilibrium if what?
The forces acting upon it are balanced
What can you split a force into?
Components
Why do you sometimes split forces into components?
Not all forces act horizontally or vertically - some act at awkward angles
To make these easier to deal with, we split them into two components at right angles to each other
Acting together, these components have the same effect as the single force
