Section 4 - Forces and Energy Flashcards
What is a system?
A single or group of objects
What happenes when a system changes?
Energ is transferred
What is a closed system?
A system with no net change in energy
How can energy be transferred?
Heat
Force
Electricity
Describe the energy transfers that occur when the wind causes a windmall to spin?
The wind does work on the windmill causing it to turn and transferring energy to the kinetic energy store of the windmill
What is the work done equation?
E = F x d Energy = Force x Distance
What does 1 J equal?
1 Nm
What does a force doing work often result in?
A rise in temperature
What is power?
How much work is done per second (rate of energy transfer)
What is the equation for power?
P = E / t Power = Energy / Time
If an electric heater has a power of 600W and it is left on for 3 seconds, how much energy is transferred?
P = E / t E = P x t E = 600 x 3 E = 1800 J
A motor does 4.8 kJ of work in 2 minutes
Find its power output?
4.8 kJ = 4800 J
P = E / t P = 4800 / 120 P = 40 W
A constant force of 20 N pushes an object 20 cm
Calculate the work done
E = F x d E = 20 x 0.2 E = 4 J
An appliance transfers 6000 J of energy in 30 seconds
Calculate its power
P = E / t P = 6000 / 30 P = 200 W
What do interactions between objects cause?
Forces
What are interaction pairs?
A pair of forces that are equal but opposite
What does a free body force diagram show?
An object and all the forces acting on it
What should free body force diagrams include?
Every force acting on the body