# Force and gravity relationship

### Gravity and the Normal Force

Gravity is a very simple force: it causes an attraction between all bodies which contain mass. The strength of the attraction between two bodies is given by. Study the solar system and how gravitational forces work with BBC Bitesize KS3 Science. Gravity and Mass. Mass v. Force. From the graph we can see that as the mass This relationship is true in all cases: as the distance increases.

The "Copernican Revolution" placed the sun at the center of the solar system and the planets, including Earth, in orbit around the sun. This major shift in perception laid the foundation for Isaac Newton to begin thinking about gravitation as it related to the motions of the planets.

Isaac Newton 's breakthrough was not that apples fall to Earth because of gravity; it was that the planets are constantly falling toward the sun for exactly the same reason: Newton built upon the work of early astronomers, in particular Johannes Keplerwho in and published his laws of planetary motion. One of Kepler's central observations was that the planets move in elliptical orbits around the sun.

Gravity, Universal Gravitation Constant - Gravitational Force Between Earth, Moon & Sun, Physics

Newton expanded Kepler's description of planetary motion into a theory of gravitation. Comprehension Checkpoint What was Newton's most important contribution to our understanding of gravity?

### Gravity | Physics | Visionlearning

Apples fall to Earth because of gravity. Planets are drawn to the sun because of gravity.

Newton's Law of Universal Gravitation The essential feature of Newton's Law of Universal Gravitation is that the force of gravity between two objects is inversely proportional to the square of the distance between them.

Such a connection is known as an "inverse square" relationship. Newton derived this relationship from Kepler's assertion that the planets follow elliptical orbits.

• Newton's Laws and Weight, Mass & Gravity
• Mass and force
• Gravity: Newtonian Relationships

To understand this, consider the light radiating from the surface of the sun. The light has some intensity at the surface of the sun.

### Types of Forces

As the light travels away from the sun, its intensity diminishes. The intensity of the light at any distance away from the sun equals the strength of the source divided by the surface area of a sphere surrounding the sun at that radius. As the distance away from the sun r doubles, the area of the sphere surrounding the sun quadruples. Thus, the intensity of the sun's light depends inversely on the square of the distance away from the sun. Newton envisioned the gravitational force as radiating equally in all directions from a central body, just as sunlight in the previous example.

Newton recognized that his gravitational model must take the form of an inverse square relationship. Such a model predicts that the orbits of objects around a central body will be conic sectionsand years of astronomical observations have borne this out.

Mass refers to how much stuff is present in the object. Weight refers to the force with which gravity pulls upon the object. Even on the surface of the Earth, there are local variations in the value of g that have very small effects upon an object's weight. These variations are due to latitude, altitude and the local geological structure of the region.

Use the Gravitational Fields widget below to investigate how location affects the value of g. Sliding versus Static Friction As mentioned abovethe friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it.

For the purpose of our study of physics at The Physics Classroom, there are two types of friction force - static friction and sliding friction.

Sliding friction results when an object slides across a surface. As an example, consider pushing a box across a floor. The floor surface offers resistance to the movement of the box. We often say that the floor exerts a friction force upon the box. This is an example of a sliding friction force since it results from the sliding motion of the box.

If a car slams on its brakes and skids to a stop without antilock brakesthere is a sliding friction force exerted upon the car tires by the roadway surface. This friction force is also a sliding friction force because the car is sliding across the road surface. Sliding friction forces can be calculated from knowledge of the coefficient of friction and the normal force exerted upon the object by the surface it is sliding across.

## Types of Forces

The coefficient value is dependent primarily upon the nature of the surfaces that are in contact with each other.

For most surface combinations, the friction coefficients show little dependence upon other variables such as area of contact, temperature, etc. The more that surface molecules tend to adhere to each other, the greater the coefficient values and the greater the friction force. Friction forces can also exist when the two surfaces are not sliding across each other. Such friction forces are referred to as static friction.

## Astronomy and space science

Static friction results when the surfaces of two objects are at rest relative to one another and a force exists on one of the objects to set it into motion relative to the other object. Suppose you were to push with 5-Newton of force on a large box to move it across the floor.

The box might remain in place. A static friction force exists between the surfaces of the floor and the box to prevent the box from being set into motion. The static friction force balances the force that you exert on the box such that the stationary box remains at rest.

When exerting 5 Newton of applied force on the box, the static friction force has a magnitude of 5 Newton.

Suppose that you were to push with 25 Newton of force on the large box and the box were to still remain in place. Static friction now has a magnitude of 25 Newton. Then suppose that you were to increase the force to 26 Newton and the box finally budged from its resting position and was set into motion across the floor. The box-floor surfaces were able to provide up to 25 Newton of static friction force to match your applied force. Yet the two surfaces were not able to provide 26 Newton of static friction force.

The amount of static friction resulting from the adhesion of any two surfaces has an upper limit.