Work and energy
Mass is a measure of the amount of material in an object, weight is the gravitational force acting on a body (although for trading purposes it is. To find the force of impact, you need to know kinetic energy (mass x 1/2 x velocity squared) and distance over which the impact took place. In general, the energy transferred depends on the amount of force and the distance If you lift kg of mass 1-meter, you will have done Joules of work.
Many students of physics confuse weight with mass. The mass of an object refers to the amount of matter that is contained by the object; the weight of an object is the force of gravity acting upon that object. Mass is related to how much stuff is there and weight is related to the pull of the Earth or any other planet upon that stuff. The mass of an object measured in kg will be the same no matter where in the universe that object is located.
Mass is never altered by location, the pull of gravity, speed or even the existence of other forces. For example, a 2-kg object will have a mass of 2 kg whether it is located on Earth, the moon, or Jupiter; its mass will be 2 kg whether it is moving or not at least for purposes of our study ; and its mass will be 2 kg whether it is being pushed upon or not.
How to Calculate Force of Impact | Sciencing
On the other hand, the weight of an object measured in Newton will vary according to where in the universe the object is. Weight depends upon which planet is exerting the force and the distance the object is from the planet.
Weight, being equivalent to the force of gravity, is dependent upon the value of g - the gravitational field strength. On earth's surface g is 9. On the moon's surface, g is 1.
Go to another planet, and there will be another g value. Furthermore, the g value is inversely proportional to the distance from the center of the planet. So if we were to measure g at a distance of km above the earth's surface, then we would find the g value to be less than 9. The nature of the force of gravity will be discussed in more detail in a later unit of The Physics Classroom.
Always be cautious of the distinction between mass and weight. It is the source of much confusion for many students of physics.
Flickr Physics Photo A 1. The scale reads just short of 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.
Force, Mass, Acceleration and How to Understand Newton's Laws of Motion
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.
It is energy associated with a moving object, in other words. For an object traveling at a speed v and with a mass m, the kinetic energy is given by: The work-energy principle There is a strong connection between work and energy, in a sense that when there is a net force doing work on an object, the object's kinetic energy will change by an amount equal to the work done: Note that the work in this equation is the work done by the net force, rather than the work done by an individual force.
Gravitational potential energy Let's say you're dropping a ball from a certain height, and you'd like to know how fast it's traveling the instant it hits the ground. You could apply the projectile motion equations, or you could think of the situation in terms of energy actually, one of the projectile motion equations is really an energy equation in disguise. If you drop an object it falls down, picking up speed along the way. This means there must be a net force on the object, doing work.
This force is the force of gravity, with a magnitude equal to mg, the weight of the object. The work done by the force of gravity is the force multiplied by the distance, so if the object drops a distance h, gravity does work on the object equal to the force multiplied by the height lost, which is: An object with potential energy has the potential to do work.
In the case of gravitational potential energy, the object has the potential to do work because of where it is, at a certain height above the ground, or at least above something. Spring potential energy Energy can also be stored in a stretched or compressed spring. An ideal spring is one in which the amount the spring stretches or compresses is proportional to the applied force.
This linear relationship between the force and the displacement is known as Hooke's law. For a spring this can be written: The larger k is, the stiffer the spring is and the harder the spring is to stretch. If an object applies a force to a spring, the spring applies an equal and opposite force to the object.
This is a restoring force, because when the spring is stretched, the force exerted by by the spring is opposite to the direction it is stretched. This accounts for the oscillating motion of a mass on a spring. If a mass hanging down from a spring is pulled down and let go, the spring exerts an upward force on the mass, moving it back to the equilibrium position, and then beyond.
This compresses the spring, so the spring exerts a downward force on the mass, stopping it, and then moving it back to the equilibrium and beyond, at which point the cycle repeats. This kind of motion is known as simple harmonic motion, which we'll come back to later in the course.