Metallizing How to Control Corrosion by Improving Design. Why is Stainless Steel Corrosion Resistant? An Introduction to Hydrogen Embrittlement. An Intro to Pipeline Corrosion in Seawater. Follow Connect with us. Sign up. Thank you for subscribing to our newsletter! Connect with us. Kinetic friction is never greater than static friction. More force is always requires to overcome static friction than is required to overcome kinetic friction.
It can require a large force to initiate motion, causing an initial acceleration by overcoming static friction. Once motion has begun, however, less for is required to maintain the motion due to the principles of Newton's first law and inertia. If you've found an issue with this question, please let us know. With the help of the community we can continue to improve our educational resources. If Varsity Tutors takes action in response to an Infringement Notice, it will make a good faith attempt to contact the party that made such content available by means of the most recent email address, if any, provided by such party to Varsity Tutors.
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Hanley Rd, Suite St. Louis, MO Subject optional. Email address: Your name:. Example Question 1 : Understanding Frictional Force. Possible Answers:. Correct answer:. Explanation : The equation for the force of friction is , where is the coefficient of static friction. The coefficient of friction has no units. Report an Error. Example Question 2 : Understanding Frictional Force.
Example Question 3 : Understanding Frictional Force. What is the coefficient of kinetic friction on the crate? Explanation : The equation for the force due to friction is , where is the coefficient of kinetic friction.
The problem gives us the mass of the crate, but we have to solve for the acceleration. Plug in our given values and solve. Students should be encouraged to consider how dependant their world is on the beneficial action of friction.
Encourage students to consider both the positive and negative effects of friction on their everyday actions and experiences. Ask students to identify what actions and tasks we do easily because of friction and what actions and tasks are made more difficult for example, consider walking, surfing and snow skiing.
The idea that surfaces have tiny bumps provides a useful model for explaining the cause and effect of friction. Students should discuss this model in an attempt to build an understanding of what the microscopic surfaces may look like and how they interact with each other. Highly magnified images of filter paper, toilet paper and rubber may be a useful discussion aid and can be seen at the following site:.
Students should be encouraged to explain why, in terms of the model of surface bumps pushing against each other, applying oil or lubricant to the contact surfaces can reduce the friction and allow them to move more freely. Students should be encouraged to identify in which direction the friction force acts in a variety of simple situations and consider examples of everyday situations where friction is deliberately increased and reduced.
A good discussion example is the purpose of using hand grips and engine oil lubricants. Students should be introduced to a variety of familiar situations involving friction where there is a focus on exploiting a frictional variation which may not be immediately apparent to students. All objects upon earth experience a force of gravity that is directed "downward" towards the center of the earth.
The force of gravity on earth is always equal to the weight of the object as found by the equation:. Caution: do not confuse weight with mass. 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.
The 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. Though 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:. The friction force is discussed in more detail later on this page. The air resistance is a special type of frictional force that acts upon objects as they travel through the air. The force of air resistance is often observed to oppose the motion of an object.
This force will frequently be neglected due to its negligible magnitude and due to the fact that it is mathematically difficult to predict its value. It is most noticeable for objects that travel at high speeds e. Air resistance will be discussed in more detail in Lesson 3. The tension force is the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire.
The spring force is the force exerted by a compressed or stretched spring upon any object that is attached to it. An object that compresses or stretches a spring is always acted upon by a force that restores the object to its rest or equilibrium position. For most springs specifically, for those that are said to obey " Hooke's Law " , the magnitude of the force is directly proportional to the amount of stretch or compression of the spring.
A few further comments should be added about the single force that is a source of much confusion to many students of physics - the force of gravity. As mentioned above , the force of gravity acting upon an object is sometimes referred to as the weight of the object.
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.
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