What do friction and gravity have in common

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. As mentioned above , the 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 brakes , there 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. The formula is:.

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. 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.

In this case, the static friction force spans the range from 0 Newton if there is no force upon the box to 25 Newton if you push on the box with 25 Newton of force. This relationship is often expressed as follows:. Like the coefficient of sliding friction, this coefficient is dependent upon the types of surfaces that are attempting to move across each other.

In general, values of static friction coefficients are greater than the values of sliding friction coefficients for the same two surfaces. Thus, it typically takes more force to budge an object into motion than it does to maintain the motion once it has been started. The meaning of each of these forces listed in the table above will have to be thoroughly understood to be successful during this unit. Ultimately, you must be able to read a verbal description of a physical situation and know enough about these forces to recognize their presence or absence and to construct a free-body diagram that illustrates their relative magnitude and direction.

See Answer b. Generally, people diet because they wish to reduce the amount of matter on their body - they wish to remove the blubber. So people diet to lose mass. If one wishes to lose weight, they could get a six fold reduction by moving to the moon.

Physics Tutorial. My Cart Subscription Selection. Student Extras. Flickr Physics Photo. We Would Like to Suggest Sometimes it isn't enough to just read about it. You have to interact with it! And that's exactly what you do when you use one of The Physics Classroom's Interactives. We would like to suggest that you combine the reading of this page with the use of our Free-Body Diagram Interactive.

You can find it in the Physics Interactives section of our website. The Free-Body Diagram Interactive allows a learner to practice identifying the forces that act upon an object and to express such an understanding by the construction of a free-body diagram.

Visit: Free-Body Diagram. See Answer 9. See Answer 0. See Answer Generally, people diet because they wish to reduce the amount of matter on their body - they wish to remove the blubber. Thus, friction is the force that opposes sliding motion, explains the Cornell Center for Materials Research. An example of friction involves removing a stain from clothing.

You place detergent on a stained shirt, then repeatedly slide part of the shirt against the stained section. The friction eliminates the stain from the shirt. Gravity is simply defined as what goes up must come down. Gravity is the natural force exerted between two objects, drawing them toward each other. Therefore, instead of an object such as an apple thrown in the air staying there or floating, it falls down. Weight is extremely important to gravity. Gravity always exerts a force equal to the weight of the object it is acting on.

A cup remains on a table because the upward force of the table is equal to the weight of the cup, causing it to stay in place. Pull affects gravity and friction in different ways. Gravity always pulls objects such as a desk, book or person down.

Thus, when you jump, gravity causes you to land on the ground. Instead friction occurs when something like a machine or individual pulls a sliding object in the opposite direction of another object. For example, when creating friction to start a fire, you repeatedly pull one stick up and the other down. Also, friction always acts parallel to the surface in contact because of the sliding action. Friction consists of two types: kinetic and static.

Kinetic friction involves movement, and static involves no movement.