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Jai Ganesh

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Registered: 2005-06-28

Posts: 50,518

Impulse

Impulse

Gist

To do something on (an) impulse or on a sudden impulse is to do it suddenly and without thinking about it first. He bought a new camera on impulse.

Impulse is the change of momentum of an object when the object is acted upon by a force for an interval of time. So, with impulse, you can calculate the change in momentum, or you can use impulse to calculate the average impact force of a collision.

The impulse of a force is a measure of the total effect of force. Impulse is a vector quantity and its direction is the same as that of force. SI unit of impulse is Newton-second or kg-m-{s}^{-1} and CGS unit is g.m/s.

Summary

Impulse has the same units and dimensions (ML{T}^{-1}) as momentum. In the International System of Units, these are kg⋅m/s = N⋅s. In English engineering units, they are slug⋅ft/s = lbf⋅s.

The term "impulse" is also used to refer to a fast-acting force or impact. This type of impulse is often idealized so that the change in momentum produced by the force happens with no change in time. This sort of change is a step change, and is not physically possible. However, this is a useful model for computing the effects of ideal collisions (such as in videogame physics engines). Additionally, in rocketry, the term "total impulse" is commonly used and is considered synonymous with the term "impulse".

Details

Impulse is a physical phenomenon that occurs whenever two objects collide with each other or when objects come into contact. When a soccer player kicks the ball or when cars crash into each other, each object experiences an impulse. All objects in motion possess momentum. The property of momentum combines on object's mass with its volume. In fact, momentum is equal to the product of an object's mass and its velocity. So, no matter how large or massive an object is, if it is not moving. it has no momentum because its velocity equals zero. The more mass an object has, the more momentum it has. Likewise, the greater the velocity of an object is, the more momentum the object has. So, a large truck has more momentum than a small car if both are traveling at the same speed. Likewise, an elephant has more momentum than smaller animals, as long as they are traveling at the same speed.

Momentum, denoted p, is shown in the diagram. Each sphere in the diagram has mass (m) and velocity (v) represented by vector symbols indicating that they have magnitude and direction. The larger sphere has more momentum even while the velocities are equal.

If momentum is the product of mass and velocity, then what is impulse? When an object with momentum encounters a force, that force changes the object's momentum. Impulse is defined as the change in the amount of momentum. Momentum changes as a result of the force interaction between the two objects. The force only need act on the object for a short period of time.

Impulse in Physics is a term that is used to describe or quantify the effect of force acting over time to change the momentum of an object. It is represented by the symbol J and is usually expressed in Newton seconds or kg m/s.

Here, we will discuss the concept of impulse in detail and understand how it is applied to different situations. Students will also learn the relation between impulse and momentum, along with suitable examples.

Before we learn what is impulse in detail, let us understand the concept of momentum.

Momentum

The term momentum is commonly used in sports. When a commentator says that a player has momentum, it means that the player is actually on the move, and it is very difficult for them to stop. A body that has momentum cannot be stopped, and therefore it is mandatory to apply a force against its direction of motion for a particular period of time. The greater the momentum, the harder it is to stop. Hence, a higher amount of force is required, and considerable time should be spent to bring the body to a halt. As the force acts on the body for a given time, the body’s velocity changes, and hence the body’s momentum changes.

A force changes the velocity of an object in either way. Also, if the object’s velocity changes, the momentum also changes.

Impulse Equation

Impulse is often stated to be the product of the average net force that acts on an object for a certain duration. The equation for impulse is given as,

J = F⋅Δt

Note: We assume that force is constant over time.

Impulse is a vector quantity like force, and it also has direction.

Newton’s Second Law

According to Newton’s second law, i.e., F = ma. An acceleration of a body is directly proportional to the net force that acts on the body and inversely proportional to the mass. If combined with the acceleration
[a = (v / t)], the resultant equation is described as:

F = m • a

or

F = m (v / t)

When both sides of the equation are multiplied by t, a new equation formed is expressed as:

F t = mv

The above equation describes one of the two primary principles to be applied in the analysis of the collision. According to the Physics textbook, the impulse is defined as the change in momentum calculated by multiplying force by time. Since momentum is mass multiplied by velocity, the quantity m•? v equals to change in momentum.

You need to understand the physics behind collisions. The collisions are based on the laws of momentum, and the first law is described in the above equation, known as the change in impulse equation.

The body experiences a force in a collision for a particular period of time and results in a change of momentum. The impact of the force acting for a particular amount of time is that the body either slows down or speeds up, or changes its direction.

The object experiences an impulse in a collision, and this impulse is equal to the change in momentum. For instance, a football halfback who is running down the field and encounters a collision with a defensive back. The collision changes the halfback’s speed and, therefore, his momentum.

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