## An Interaction That Causes A Change In An Object’s Motion

- M.S., Mathematics Education, Indiana University
- B.A., Physics, Wabash College

Force is a quantitative description of an interaction that causes a change in an object’s motion. An object may speed up, slow down, or change direction in response to a force. Put another way, force is any action that tends to maintain or alter the motion of a body or to distort it. Objects are pushed or pulled by forces acting on them.

Contact force is defined as the force exerted when two physical objects come in direct contact with each other. Other forces, such as gravitation and electromagnetic forces, can exert themselves even across the empty vacuum of space.

## Development Of The Concept

Philosophers in antiquity used the concept of force in the study of stationary andmoving objects and simple machines, but thinkers such as Aristotle and Archimedes retained fundamental errors in understanding force. In part this was due to an incomplete understanding of the sometimes non-obvious force of friction, and a consequently inadequate view of the nature of natural motion. A fundamental error was the belief that a force is required to maintain motion, even at a constant velocity. Most of the previous misunderstandings about motion and force were eventually corrected by Galileo Galilei and Sir Isaac Newton. With his mathematical insight, Sir Isaac Newton formulated laws of motion that were not improved for nearly three hundred years. By the early 20th century, Einstein developed a theory of relativity that correctly predicted the action of forces on objects with increasing momenta near the speed of light, and also provided insight into the forces produced by gravitation and inertia.

Aristotelian physics began facing criticism in medieval science, first by John Philoponus in the 6th century.

In the early 17th century, before Newton’s Principia, the term “force” was applied to many physical and non-physical phenomena, e.g., for an acceleration of a point. The product of a point mass and the square of its velocity was named *vis viva* by Leibniz. The modern concept of force corresponds to the Newton’s *vis motrix* .

## The 4 Fundamental Forces Of Physics

- M.S., Mathematics Education, Indiana University
- B.A., Physics, Wabash College

The fundamental forces of physics are the ways that individual particles interact with each other. It turns out that every single interaction observed taking place in the universe can be broken down and described by only four types of interactions:

- Weak Interaction
- Strong Interaction

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## Development Of The Force Concept

A quantitative definition of force can be based on some standard force, just as distance is measured in units relative to a standard length. One possibility is to stretch a spring a certain fixed distance ) and use the force it exerts to pull itself back to its relaxed shapecalled a **restoring force**as a standard. The magnitude of all other forces can be considered as multiples of this standard unit of force. Many other possibilities exist for standard forces. Some alternative definitions of force will be given later in this chapter.

Lets analyze force more deeply. Suppose a physics student sits at a table, working diligently on his homework ). What external forces act on him? Can we determine the origin of these forces?

In most situations, forces are grouped into two categories: **contact forces** and **field forces**. As you might guess, contact forces are due to direct physical contact between objects. For example, the student in Figure \ experiences the contact forces \, \, and \, which are exerted by the chair on his posterior, the floor on his feet, and the table on his forearms, respectively. Field forces, however, act without the necessity of physical contact between objects. They depend on the presence of a field in the region of space surrounding the body under consideration. Since the student is in Earths gravitational field, he feels a gravitational force \ in other words, he has weight.

## Why Is It Easier To Open The Lid Of A Container With A Spoon Than A Coin

**Show/hide answer**

A spoon is longer than a coin. If you use them to open the lid of a container by pivoting, the perpendicular distance will be longer for a spoon than a coin.

Lets assume that it takes an $x \text$ of moment of a force to open the lid and that $d_} = 2 d_}$.

Find amount of force needed to open the lid if we use a **spoon**:

$$\begin r & = F \times d \\ x & = F_} \times d_} \\ F_} & = \frac}} \end$$

Find amount of force needed to open the lid if we use a **coin**:

$$\begin r & = F \times d \\ x & = F_} \times d_} \\ F_} & = \frac}} \end$$

Since $d_} = 2 d_}$,

$$\begin F_} & = \frac}}} \\ & = 2 \frac}} \\ & = 2 F_} \end$$

From the calculations above , you will need twice as much force to open the lid of a container if you use a coin.

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## Solved Examples On Force Formula

**Example 1.** A constant force acting on a body of mass 3.0 kg changes its speed from 2.0 m/s to 3.5m/s in 25 s. The direction of the motion of the body does not changes. What is the magnitude and what is the direction of the force?

**Solution**

Mass of the body, m = 3 kgInitial speed of body, u = 2 m/sFinal speed of body, v = 3.5 m/sTime, t = 25 s

Using the first equation of motion, the acceleration produced in the body can be calculated as:

v = u+at

F = ma

= 3 × 0.06 = 0.18 N

Since the application of the force does not change the direction of the body, the net force acting on the body goes in the direction of its motion.

**Example 2.** A stream of water flowing horizontally with a speed \ of gushes out of a tube of cross-sectional area \, and hits a vertical wall nearby. What is the force exerts on the wall by the waters impact, assuming it does not rebound?

**Solution**

Speed of water stream, v = 15 m/sThe cross-sectional area of the tube, A = 10 mThe volume of water that comes out through the pipe per second,V = A x v = 15 x 10 m /sDensity of water, = 10 kg/mMass of water that flows out in the pipe per second = density V = 150 kg/sThe water hits the wall and doesnt rebound. Therefore, the force that the water exerts on the wall is given by

Newtons second law of motion as:F = Rate of change of momentum = P / t.= mv / t= 150 x 15 = 2250 N

## Working Definition Of Force

Dynamics is the study of the forces that cause objects and systems to move. To understand this, we need a working definition of force. An intuitive definition of **force**that is, a push or a pullis a good place to start. We know that a push or a pull has both magnitude and direction , so we can define force as the push or pull on an object with a specific magnitude and direction. Force can be represented by vectors or expressed as a multiple of a standard force.

The push or pull on an object can vary considerably in either magnitude or direction. For example, a cannon exerts a strong force on a cannonball that is launched into the air. In contrast, Earth exerts only a tiny downward pull on a flea. Our everyday experiences also give us a good idea of how multiple forces add. If two people push in different directions on a third person, as illustrated in Figure \, we might expect the total force to be in the direction shown. Since force is a vector, it adds just like other vectors. Forces, like other vectors, are represented by arrows and can be added using the familiar head-to-tail method or trigonometric methods. These ideas were developed in Vectors.

Problem-Solving Strategy: Drawing Free-Body Diagrams

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## What Is A Field Force In Physics

**Field forces****forces****Field forces****forces****forces****field forces****forces****force****force**

. Also to know is, what is field force with example?

A **force field** in physics is a map of a **force** over a particular area of space. **Examples** of **force fields** include magnetic **fields**, gravitational **fields**, and electrical **fields**.

Additionally, what are the types of field in physics? **Classical fields**

- Newtonian gravitation.
- Continuous random fields.

Also to know is, what is meant by a field in physics?

**Field, In physics**, a region in which each point is affected by a force. Objects fall to the ground because they are affected by the force of earth’s gravitational **field** . See also electromagnetic **field**.

What are contact forces in physics?

A **contact force** is any **force** that requires **contact** to occur. **Contact forces** are ubiquitous and are responsible for most visible interactions between macroscopic collections of matter. Molecular and quantum **physics** show that the electromagnetic **force** is the fundamental interaction responsible for **contact forces**.

## Contact Vs Noncontact Force

There are two types of forces in the universe: contact and noncontact. Contact forces, as the name implies, take place when objects touch each other, such as kicking a ball: One object touches the other object . Noncontact forces are those where objects do not touch each other.

Contact forces can be classified according to six different types:

**Tensional:**such as a string being pulled tight**Spring:**such as the force exerted when you compress two ends of a spring**Normal reaction:**where one body provides a reaction to a force exerted upon it, such as a ball bouncing on a blacktop**Friction:**the force exerted when an object moves across another, such as a ball rolling over a blacktop**Air friction:**the friction that occurs when an object, such as a ball, moves through the air**Weight:**where a body is pulled toward the center of the Earth due to gravity

Noncontact forces can be classified according to three types:

**Gravitational:**which is due to the gravitational attraction between two bodies**Electrical:**which is due to the electrical charges present in two bodies**Magnetic:**which occurs due to the magnetic properties of two bodies, such as the opposite poles of two magnets being attracted to each other

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## What Is The Line Of Action Of A Force

The line along which a force is acting on an object is called the **line of action of the force**. The point where the force is acting on an object is called the point of **application of the force**. The force which opposes the relative motion between the surfaces of two objects in contact and acts along the surfaces is called the force of friction.

Galileo experimentally proved that objects that are in motion move with constant speed when there is no force acting on it. He could note that when a sphere is rolling down an inclined plane, its speed increases because of the gravitational pull which is acting on it.

When all the forces acting on an object are balanced, the net force acting is zero. But, if all the forces acting on a body result in an unbalanced force, then the unbalanced force can accelerate the body, which means that a net force acting on a body can either change the magnitude of its velocity or change the direction of its velocity. For example, when many forces act on a body, and the body is found to be at rest, we can conclude that the net force acting on the body is zero.

## What Is Normal Force

Normal force is **the perpendicular force that the surface exerts on an object**. For example, if you put a book on a table, there is a gravitational force that is pulling it toward the ground. To counteract this force, the table exerts a force on the book, preventing it from falling. This counteracting force is called the *normal force*, and is represented by FN, or N. The unit for the normal force is ‘*N*‘ .

The normal force is a typical example of the Newton’s third law of motion.

If one object exerts a force on a second object, the second object exerts a force of equal magnitude and opposite direction on the first object .

So, a normal force is equal to the force exerted by the object on the surface. It’s formulas vary with the slope of the surface.

FN = m * g

- m is the mass of an object.
- g is the gravitational acceleration.

According to Newton’s third law, the normal force for an object on a flat surfaces is equal to its gravitational force .

FN = m * g * cos

- is the surface inclination angle .

On an inclined surface , the weight of the object is supported by both the normal force and friction. The gravitational force of the object is not opposite and equal to the normal force, but one of the force of gravity’s vector’s components is.

To find out how to calculate normal force with friction, use the friction calculator.

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## Force And Newton’s Laws Of Motion

The concept of force was originally defined by Sir Isaac Newton in his three laws of motion. He explained gravity as an attractive force between bodies that possessed mass. However, gravity within Einstein’s general relativity doesn’t require force.

**Newton’s First Law of Motion** says that an object will continue to move at a constant velocity unless it is acted upon by an external force. Objects in motion remain in motion until a force acts on them. This is inertia. They won’t speed up, slow down, or change direction until something acts on them. For example, if you slide a hockey puck, it will eventually stop because of friction on the ice.

**Newton’s Second Law of Motion** says that force is directly proportional to acceleration for a constant mass. Meanwhile, acceleration is inversely proportional to mass. For example, when you throw a ball thrown onto the ground, it exerts a downward force the ground, in response, exerts an upward force causing the ball to bounce. This law is useful for measuring forces. If you know two of the factors, you can calculate the third. You also know that if an object is accelerating, there must be a force acting on it.

## Key Takeaways: Key Terms

**Force:**A description of an interaction that causes a change in an object’s motion. It can also be represented by the symbol*F.***The Newton:**The unit of force within the International system of units . It can also be represented by the symbol*N.***Contact forces:**Forces which take place when objects touch each other. Contact forces can be classified according to six types: tensional, spring, normal reaction, friction, air friction, and weight.**Noncontact forces:**Forces that take place when two objects do not touch. These forces can be classified according to three types: gravitational, electrical, and magnetic.

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## Forces In Quantum Mechanics

The notion “force” keeps its meaning in quantum mechanics, though one is now dealing with operators instead of classical variables and though the physics is now described by the SchrÃ¶dinger equation instead of Newtonian equations. This has the consequence that the results of a measurement are now sometimes “quantized”, i.e. they appear in discrete portions. This is, of course, difficult to imagine in the context of “forces”. However, the potentials *V* or fields, from which the forces generally can be derived, are treated similarly to classical position variables, i.e., V }} .

This becomes different only in the framework of quantum field theory, where these fields are also quantized.

Thus the notion “force” loses already part of its meaning.

The utility of Feynman diagrams is that other types of physical phenomena that are part of the general picture of fundamental interactions but are conceptually separate from forces can also be described using the same rules. For example, a Feynman diagram can describe in succinct detail how a neutron into an electron, proton, and neutrino, an interaction mediated by the same gauge boson that is responsible for the weak nuclear force.

**The four fundamental forces of nature**

Property/Interaction |
---|

, is the unit vector directed outward from the center of the Earth.

- E

## Unifying The Fundamental Forces

Many physicists believe that all four of the fundamental forces are, in fact, the manifestations of a single underlying force which has yet to be discovered. Just as electricity, magnetism, and the weak force were unified into the electroweak interaction, they work to unify all of the fundamental forces.

The current quantum mechanical interpretation of these forces is that the particles do not interact directly, but rather manifest virtual particles that mediate the actual interactions. All of the forces except for gravity have been consolidated into this “Standard Model” of interaction.

The effort to unify gravity with the other three fundamental forces is called *quantum gravity*. It postulates the existence of a virtual particle called the graviton, which would be the mediating element in gravity interactions. To date, gravitons have not been detected, and no theories of quantum gravity have been successful or universally adopted.

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