A force is a push or pull upon an object resulting from the object's interaction with another object, either concerning its movement, direction, or geometrical construction. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction. For simplicity sake, all forces (interactions) between objects can be placed into two broad categories:contact forces, andforces resulting from action-at-a-distanceContact forces are those types of forces that result when the two interacting objects are perceived to be physically contacting each other. Examples of contact forces include frictional forces tensional forces normal forces air resistance forcesapplied forcesAction-at-a-distance forces are those types of forces that result even when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation. Examples of action-at-a-distance forces include gravitational forces. For example, the sun and planets exert a gravitational pull on each other despite their large spatial separation. Even when your feet leave the earth and you are no longer in physical contact with the earth, there is a gravitational pull between you and the Earth. Electric forces and magnetic forces are action-at-a-distance forces.

Gravitational force /Force of gravityNewtons Law of Universal Gravitation states that every massive particle in the universe attracts every other massive particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. Mathematically this can be written as:

Where M1 and M2 are two masses and r is the distance between them.G is called the universal gravitational constant of gravitation as is equal to 6.67x10-11Nm2kg-2

Centripetal forceCenter-seeking force exerted that allows an object to move in a curved path by a force that acts towards the center. This can comes from

Pull of stringGravityMagnetismFriction

If a mass is accelerating, it must have a force acting on it; centripetal Force, Fc = mac = mv/rac = centripetal acceleration (m/s)v = velocity (m/s)r = radius (m)When centripetal force equals gravitational force the object stays in orbit GmM/r = mvo/r

The source for the centripetal force in the solar system is the gravitational force of the sun. Without the centripetal force from the sun the planets would travel in a straight line. The velocity of the planets is high enough so that they continuously accelerate towards the sun without ever leaving their orbits. It is for this reason that the planets do not fall into the sun from its strong gravitational force of attraction

Notice that the gravitational force is directly proportional to m1. Thus, all things being equal, a more massive planet would exert a larger gravitational force than a smaller planet. Hence, youll be heavier on Jupiter than here on Earth.

Notice that the gravitational force is also directly proportional to m2. Thus, all things being equal again, you would weigh more than a puppy.

Notice that the force of gravity is inversely proportional to the square of r. Thus, all things being equal again, you would feel heavier on the surface of the Earth than on say, a hot air balloon at high altitudes. Notice that since F is inversely proportional to the square of r, F would vary rapidly for a slight change in r. Thus, if you go even further from the Earths surface, say on a satellite, F would decrease rapidly and even become negligible.

Gravitational force surrounds us. It is what decides how much we weigh and how far a basketball will travel when thrown before it returns to the surface. The gravitational force on Earth is equal to the force the Earth exerts on you. At rest, on or near the surface of the Earth, the gravitational force equals your weight. On a different astronomical body like Venus or the Moon, the acceleration of gravity is different than on Earth, so if you were to stand on a scale, it would show you that you weigh a different amount than on Earth.In our day to day lives, we can measure the force of gravity. Its more familiar term is weight. Thus, in most cases , your measured weight is actually a measurement of the force of the Earths gravity on you. The heavier you are, the greater is the force of gravity on you. There are exceptions, like when you are buoyed up by a fluid but that is for another text

If the gravitational pull of the Moon were the same over all parts of the Earth, there would be no tides on the Earth. Tides are caused by the difference in gravitational force from one part of the Earth to another. Tides are caused by stretching, and stretching is caused not by the size of the forces on an object, but by the difference in force from one part of the object to another. For instance, the stretch of a rubber band doesn't depend on how much force is exerted on the rubber band, but by the difference in force between one side of the rubber band and the other. The gravitational force between the Earth and the Sun is much greater than the gravitational force between the Earth and the Moon - after all, the Earth orbits the Sun, not the Moon! The Moon is much more effective than the Sun in raising tides on Earth because, since the Moon is closer to the Earth, it causes more difference in gravitational force from one part of the Earth to another than the Sun does. Since the Sun exerts more gravitational force, it causes more acceleration of the Earth, but since the Moon causes more difference in force, the Moon causes more tidal stretching on the Earth

Difference between G and g?G= universal gravitation constant 1. gravitational constant2. scalar quantity3. Nm2kg-24. it cannot be 05. it is the same at every place on earth

g= accelaration due to gravity

1. acceleration due to gravity....2. vector quantity..3. m/s2...4. it can be 0 at the centre of the earth..5. it is not the same in all places. it difers from place to place...

The force of gravity with which an object is attracted to the earth is calculated as below.

where d represents the distance from the center of the object to the center of the earth and m represents the mass of the object.

An equation was given for determining the force of gravity (Fgrav) with which an object of mass m was attracted to the earth and g is referred to as the acceleration of gravity.Fgrav = m*g

This leaves us with an equation for the acceleration of gravity. The above equation demonstrates that the acceleration of gravity is dependent upon the mass of the earth (approx. 5.98x1024 kg) and the distance (d) that an object is from the center of the earth. If the value 6.38x106 m (a typical earth radius value) is used for the distance from Earth's center, then g will be calculated to be 9.8 m/s2. And of course, the value of g will change as an object is moved further from Earth's center.

The table below shows the value of g at various locations from Earth's center.

The equation takes the following form: Using this equation, the following acceleration of gravity values can be calculated for the various planets.

Calculating g on Other Planets

LocationDistance from Earth's center (m)Value of g (m/s2)Earth's surface6.38 x 106 m9.81000 km above surface7.38 x 106 m7.33

PlanetRadius (m)Mass (kg)g (m/s2)Mercury2.43 x 1063.2 x 10233.61Venus6.073 x 1064.88 x10248.83Mars3.38 x 1066.42 x 10233.75

Would a ball that is dropped by an astronaut and hits the surface of the moon with a greater, equal, or lesser speed than that of a ball dropped the same distance on earth?

B) Would it take the ball more, less, or equal time to fall? A) v = (2 x g x h)^0,5 (^0,5 means the square root) this is the formula that calculates the velocity (v) at which an object will hit the ground when dropped from a certain height h) On earth , g = 9.8 m/s2 = 32.2 ft/s2 that on the moon is about 1/6 of that. A quick peak the formula will show you that on the moon it g is about a sixth so v will always be less (h being equal). Basically objects dropped on the moon do not accelerate as fast as they do on earth. B) h = 0.5g x t^2 (that's the basic equation) t^2 = h / 0.5g since h = constant and g is different (g on the moon is 1/6 of g on earth) If g is smaller on the moon, an object dropped from height h will take longer (t will be more) than an object dropped from the same height on earth.

Friction ForceThe friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it. There are at least two types of friction force - sliding and static friction. Thought it is not always the case, the friction force often opposes the motion of an object. For example, if a book slides across the surface of a desk, then the desk exerts a friction force in the opposite direction of its motion. Friction results from the two surfaces being pressed together closely, causing intermolecular attractive forces between molecules of different surfaces. As such, friction depends upon the nature of the two surfaces and upon the degree to which they are pressed together. The maximum amount of friction force that a surface can exert upon an object can be calculated using the formula below: Ffrict = Fnorm, is the coefficient of friction, which is an empirical property of the contacting materials, and Fnorm is the normal force exerted by each surface on the other, directed perpendicular (normal) to the surface.

An example of static friction is the force that prevents a car wheel from slipping as it rolls on the ground. Even though the wheel is in motion, the patch of the tire in contact with the ground is stationary relative to the ground, so it is static rather than kinetic friction.Sliding (or dynamic) friction occurs when two objects are moving relative to each other and rub together (like a sled on the ground).

The normal force is the support force exerted upon an object that is in contact with another stable object. For example, if a book is resting upon a surface, then the surface is exerting an upward force upon the book in order to support the weight of the book. On occasions, a normal force is exerted horizontally between two objects that are in contact with each other. For instance, if a person leans against a wall, the wall pushes horizontally on the person.Action reaction forcesAccording to Newton's third law, for every action force there is an equal (in size) and opposite (in direction) reaction force. Forces always come in pairs - known as "action-reaction force pairs."For example, consider the interaction between a baseball bat and a baseball.

The baseball forces the bat to the left; the bat forces the ball to the right. Together, these two forces exerted upon two different objects form the action-reaction force pair.

Examples:Baseball pushes glove leftwards.

2. Bowling ball pushes pin leftwards.

3. Enclosed air particles push balloon wall outwards.

4. Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. Since forces result from mutual interactions, the air must also be pushing the bird upwards. The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards).

5. While driving down the road, a firefly strikes the windshield of a bus and makes a quite obvious mess in front of the face of the driver. This is a clear case of Newton's third law of motion. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the bus?Answer: Each force is the same size. For every action, there is an equal ... (equal!). The fact that the firefly splatters only means that with its smaller mass, it is less able to withstand the larger acceleration resulting from the interaction. Besides, fireflies have guts and bug guts have a tendency to be splatterable. Windshields don't have guts.

5. In the top picture (below), Monir is pulling upon a rope that is attached to a wall. In the bottom picture, Monir is pulling upon a rope that is attached to an elephant. In each case, the force scale reads 500 Newton.Monir is pulling ...

a. with more force when the rope is attached to the wall.b. with more force when the rope is attached to the elephant.c. the same force in each case.Answer: CMonir is pulling with 500 N of force in each case. The rope transmits the force from Monir to the wall (or to the elephant) and vice versa. Since the force of Kent pulling on the wall and the wall pulling on Kent are action-reaction force pairs, they must have equal magnitudes. Inanimate objects such as walls can push and pull.

6. Consider the motion of a car on the way to school. A car is equipped with wheels that spin. As the wheels spin, they grip the road and push the road backwards. Since forces result from mutual interactions, the road must also be pushing the wheels forward. The size of the force on the road equals the size of the force on the wheels (or car); the direction of the force on the road (backwards) is opposite the direction of the force on the wheels (forwards). For every action, there is an equal (in size) and opposite (in direction) reaction. Action-reaction force pairs make it possible for cars to move along a roadway surface.

BrakesA brake is a mechanical device which inhibits motion. Most commonly brakes use friction to convert kinetic energy into heat, though other methods of energy conversion may be employed. For example regenerative braking converts much of the energy to electrical energy, which may be stored for later use. Other methods convert kinetic energy into potential energy in such stored forms as pressurized air or pressurized oil. Eddy current brakes use magnetic fields to convert kinetic energy into electric current in the brake disc, fin, or rail, which is converted into heat. Still other braking methods even transform kinetic energy into different forms, for example by transferring the energy to a rotating flywheel.When the brake pedal of a modern vehicle with hydraulic brakes is pushed, ultimately a piston pushes the brake pad against the brake disc which slows the wheel down.

LubricationLubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity, and moving relative to each other, by interposing a substance called lubricant between the surfaces to carry or to help carry the load (pressure generated) between the opposing surfaces. The interposed lubricant film can be a solid, (e.g. graphite, MoS2)a solid/liquid dispersion, a liquid, a liquid-liquid dispersion (a grease) or, exceptionally, a gas.

The science of friction, lubrication and wear is called tribology.

WeightlessnessThe phenomenon of "weightlessness" occurs when there is no force of support on your body. When your body is effectively in "free fall", accelerating downward at the acceleration of gravity, then you are not being supported. The sensation of apparent weight comes from the support that you feel from the floor, from the seat, etc. Different sensations of apparent weight can occur on a roller-coaster or in an aircraft because they can accelerate either upward or downward. Spacecraft are held in orbit by the gravity of the planet which they are orbiting. In Newtonian physics, the sensation of weightlessness experienced by astronauts is not the result of there being zero gravitational acceleration (as seen from the Earth), but of there being no g-force that an astronaut can feel because of the free-fall condition, and also there being zero difference between the acceleration of the spacecraft and the acceleration of the astronaut. What's missing is "weight", the resistance of gravitational attraction by an anchored structure or a counterforce.

The mass of an object is a fundamental property of the object; a numerical measure of its inertia; a fundamental measure of the amount of matter in the object.

The weight of an object is the force of gravity on the object and may be defined as the mass times the acceleration of gravity, w = mg. Since the weight is a force, its SI unit is the Newton.

In mechanics, the normal force is the component, perpendicular to the surface (surface being a plane) of contact, of the contact force exerted on an object by, for example, the surface of a floor or wall, preventing the object from penetrating the surface.**