# Concept Map

Error: Mind Map file `Universal_Law_of_Gravitation.mm` not found

# Teaching Outlines

## Concept #1 - Nature of Gravitational Force

### Learning objectives

1. Inertial and Gravitational Property of Mass
2. Idea of a force field and that forces can act at a distance. The distance over which the effect of a force can be felt is called its field.
3. Gravitational force acts over a distance through a field and is one of the four fundamental forces
4. Gravitational force is a very small force

### Notes for teachers

These are short notes that the teacher wants to share about the concept, any locally relevant information, specific instructions on what kind of methodology used and common misconceptions/mistakes.

• Mass has two aspects – inertial and gravitational. We are familiar with mass; it is an intrinsic property of matter. An intrinsic property is something that cannot be separated from the object. The mass of an object can be understood in terms of its gravitational aspect and inertial aspect. The intrinsic property of matter which makes it resist change is what we have called as mass. But this same mass possesses another property – the ability to “attract” mass. This we call the gravitational aspect. The gravitational aspect of the mass is responsible for the attractive force between two masses. The gravitational aspect is what makes masses interact with one another.
• Gravitation is a fundamental force. Gravitational force, or gravity, is the force by which physical bodies attract each other with a force directly proportional to their mass and inversely proportional to the square of the distance between them. This is one of the four fundamental forces in nature. Gravity is the force which makes masses interact with one another. Gravitational force is mutually attractive. Another fundamental force is the electromagnetic force, due to another intrinsic property of matter – charge. These forces are due to charges possessed by an object and their movement.
• Strong and weak nuclear forces are other fundamental forces that act within the nucleus of an atom, holding it together. These forces however act only at the subatomic level. Above the atomic level, gravitational and electromagnetic forces can satisfactorily explain all events.

### Activity No # 1 - Discussion about mass

• Estimated Time - 30 minutes
• Materials/ Resources needed
• Prerequisites/Instructions, if any
• Multimedia resources

This video describes the inertial property of mass

• Process (How to do the activity)
1. Let the students watch the video
2. Ask them to write situations where they have faced inertia
• Developmental Questions (What discussion questions)
1. When do we say something has inertia? (When it does not change its position)
2. What does inertia do? (Resists change)
3. Does it depend on size of the object? (Yes/ No/ Not always)
4. If not on size, what does it depend on? (It depends on how much matter ther?e is - mass)
5. When we observe inertia, we can say object has mass
• Evaluation (Questions for assessment of the child)
1. Does inertia increase with size?
2. Will an object have inertia when it moves?
• Question Corner
1. How can I tell that an object has mass or not?

### Activity No #

• Estimated Time
• Materials/ Resources needed
• Prerequisites/Instructions, if any
• Multimedia resources
• Process (How to do the activity)
• Developmental Questions (What discussion questions)
• Evaluation (Questions for assessment of the child)
• Question Corner

## Concept #2 - Newton's law of universal gravitation

### Learning objectives

1. Gravitational Force is small
2. The importance of inverse square law

### Activity 1 Use the following simulation for a demonstration of the gravitational force

 Click to Run

### Notes for teachers

These are short notes that the teacher wants to share about the concept, any locally relevant information, specific instructions on what kind of methodology used and common misconceptions/mistakes.

Inverse Square Law

Newton's law of gravitation resembles Coulomb's law of electrical forces, which is used to calculate the magnitude of electrical force between two charged bodies. Both are inverse-square laws, in which force is inversely proportional to the square of the distance between the bodies. Coulomb's Law has the product of two charges in place of the product of the masses, and the electrostatic constant in place of the gravitational constant. One important point of comparison is that the the value of the constant in Coulomb's law (for force between two charges of 1C separated by a distance of 1 m) is of the order of magnitude 109, which is 1000 billion billion times more than the gravitational constant. This means that the electrostatic force is a much stronger force than the gravitational force.

Why should this be so?

When we consider the gravitational field of a mass, we consider it to be a point mass. For any object, this can be approximated and we can find that this holds true. Some standard physics textbooks will give us this mathematical derivation as well. If there is a point mass and there is a field originating from it, the field must originate uniformly in all directions. If we imagine enclosing this point mass in a sphere and if we represent the field by field lines (called flux), we can visualize that these field lines must pass through uniformly throughout the surface area of the sphere. Now we can use simple geometry to explain why the field varies with inverse square of the distance. For the same area, the number of flux lines that will cut through a given area will reduce the farther the area is from the source. If we consider the area as a square on the surface of a sphere, the density of flux lines that will cut through the surface of a sphere is inversely proportional to the square of the distance from the source as the surface area of a sphere increases with the square of the radius. Hence the field strength will vary inversely with the square of the distance.

Law of gravitation and relativity

Newton's law has since been superseded by Einstein's theory of general relativity, but it continues to be used as it is, as an excellent approximation of the effects of gravity. Gravitational force acts at a distance. The properties of the space surrounding any massive body can be considered to be altered in such a way that another massive body in this region experiences a force. This alteration of space is a gravitational field. Einstein perceived a gravitational field as a geometrical warping of four dimensional space and time; masses “bend” the space around them. Gravity is the property of matter that possesses mass that causes a force of attraction to exist between any two particles in space.

### Activity No #

• Estimated Time
• Materials/ Resources needed
• Prerequisites/Instructions, if any
• Multimedia resources
• Process (How to do the activity)
• Developmental Questions (What discussion questions)
• Evaluation (Questions for assessment of the child)
• Question Corner

### Activity No #

• Estimated Time
• Materials/ Resources needed
• Prerequisites/Instructions, if any
• Multimedia resources