Unit 5 Work, Energy and Power Flashcards
(34 cards)
In Primary Science and Lower Secondary Science, energy is represented in _________ such as kinetic energy, potential energy, electrical energy, etc. These energy forms can be ___________________. This model is still widely used today.
First blank:
Different forms
Second blank:
Converted from one form to another through interactions with the physical world.
In this chapter, we aim to approach the energy discussion using a new model “ __________”. this model seeks to be a better way to learn about energy where it is _______________________.
With this new model of energy discussion, students will be proficient to use 2 models to describe the energy concept in Science.
Two models to represent energy:
- __________________
- __________________
First blank:
Energy stores and transfers
Second blank:
Modelled as an invisible substance that can be transferred between energy stores.
Third blank:
Energy forms and conversions
Fourth blank:
Energy stores and transfers
Why is energy required?
Energy is required for things to work.
What is the SI unit of energy?
The SI unit of energy is the joule (J).
What are the six different types of energy stores?
- Kinetic store (energy)
- Gravitational potential store
- Elastic potential store
- Chemical potential store
- Internal store
- Nuclear store
What is the description for kinetic store (energy)?
Any object in motion has energy in the kinetic store (kinetic energy).
Or
Energy in the kinetic store is the energy a body possesses due to its motion.
What is the description for gravitational potential store?
An object raised above ground has energy in the gravitational potential store (gravitational potential energy).
Energy in the potential store is the energy stored in a system because of its position of an object in a gravitational field.
What is the description for elastic potential store?
A stretched rubber band or a compressed spring has energy in the elastic potential store (elastic potential energy).
What is the description for chemical potential store?
The food we eat, fossil fuels and batteries have energy in the chemical potential store (chemical potential store)
What is the description for internal store?
A hot object, such as hot metal or a hot drink, has energy in the internal store (internal energy).
What is the description for nuclear store?
The nuclei of atoms have energy in the nuclear store (nuclear energy).
What is one analogy you can use to understand the model of energy stores and transfers?
one analogy to understand this model is to think of energy as money and energy stores as different bank accounts where money can be stored.
We can transfer money (energy) from one bank account (energy store) to another bank account (energy store) but the total amount of money is a constant.
Money (energy) can be transferred between the bank accounts (energy stores) in different ways. For example, we can transfer money using internet banking or at the Automated teller Machines (ATMs). Similarly, energy can be transferred to different energy stores through different pathways.
the energy in a system can be accounted for by discussing _________ and ____________.
Various energy stores and transfers between stores and/or systems by four pathways.
Energy can be transferred by…
(a) mechanically (by a force acting over a distance)
(B) by heating (as a result of a temperature difference)
(C) by propagation of waves (both electromagnetic and mechanical)
(D) electrically (by charges moving through a potential difference)
Add an acronym here later
Given this observation:
“The diagram below shows a cart of mass m moving horizontally at a constant speed of 1.2m/s along a smooth surface. When it is pushed by an applied force F over a short distance s, its speed increases to 2.0 m/s.
(A)
Explain this using the concept of energy transfer.
(B)
Suggest what will happen to the amount of energy of the system (cart) after the force F is applied.
(A)
in this case, energy is transferred mechanically by a force acting over a distance
Explanation:
Assuming negligible friction between the cart and the surface, the resultant force acting on the cart is the applied force F. By Newton’s Second Law of Motion, this resultant force F causes the cart to acceleration in the direction of the applied force. We will learn that when a force moves an object through a distance, mechanical work is done by force F on the cart. We will also learn that energy in the kinetic store of an object is directly proportional to the square of its speed.
Key words and concepts:
- assuming negligible friction between…
(IMPORTANT to highlight what surface an object you are referring to)
- resultant force acting on ____ is the applied force F over
- By Newton’s second law of motion (resultant force) —> link the concepts together
- highlight the type of energy transfer (mechanical work is done by force F ON the CART.
(b)
After the force is applied, the energy in the kinetic store of the system (cart) increases. The energy in its kinetic store is represented by four units.
The increase in the energy in its kinetic store is due to the mechanical work done by force F acting on the cart over the distance s.
Note that the cart is travelling on a smooth surface. As there is no friction, the energy transferred out of the system is zero.
For an object of mass m moving with velocity v, the energy in kinetic store (kinetic energy) can be given by:
E subscript k = 1/2 m v square
What is the SI unit of Ek?
SI unit of Ek: joule (J)
Ek refers to the energy in kinetic store (kinetic energy)
if we take the Earth’s surface to be the zero gravitational potential energy level, an object of mass m near to Earth raised to a height h above the Earth’s surface has increased the gravitational energy of the mass-Earth system by
(Formula)?
E subscript p = mgh
For h, it is the vertical height and not the slanted height
Ep refers to the energy in gravitational potential store (gravitational potential energy)
What is the SI unit of Ep?
SI unit of Ep: joule (J)
What are the things that you should take note regarding energy in gravitational potential store (gravitational potential energy)?
h in Ep = mgh should be the vertical height and not the slanted height
Note:
1. Only changes in energy in the gravitational potential store matters.
- The zero gravitational potential energy level can be assigned to any point that is convenient.
When a question requires you to calculate the change in the energy of the gravitational potential store in the box, what should you do?
Firstly change in the energy means
Final Ep - initial Ep
If you know the final Ep, then calculate the initial Ep using the formula Ep = mgh while ensuring that h is the vertical height
What is the principle of conservation of energy?
The principle of conservation of energy states that
- energy cannot be created nor destroyed.
- Energy can be transferred from one store to another.
- The total energy of an isolated system is constant.
We can apply the principle of conservation of energy to the _______________. In that system, (formula?)
To the total energy of an isolated system.
In an isolated system,
E initial = E final
How should you approach a work, energy and power question?
- identify the amount of energy stored
- use the formula
- create an equation
- solve for the unknown
