How is impulse different from force
That's why impulse is conceptually different than change in momentum--if a book is just resting on a table, over a given time period it will receive an impulse due to gravity and an impulse due to the normal force from the table, and these will cancel out so there is zero net change in the book's momentum.
As an analogy, if an object is traveling at constant velocity for a given time period you can multiply the velocity by the time to get the change in position during that period, but this doesn't mean a velocity is "actually" just a change in position, since velocity is the rate that position changes with time.
For example, two cars can both travel a distance of 60 miles same change in position , but if one takes an hour to do it while the other takes two hours, their velocities are different.
In the same way, two objects can both receive the same impulse, but if it took different time periods for them to receive that impulse, the forces on each object must have been different.
Realistically, all forces act over some time, although in some cases as contact forces during a collision, the force may act for only a tiny fraction of a second. In principle you could have a mathematical model of a force acting at only a single point in time but conveying a nonzero impulse using a dirac delta function , but this wouldn't accurately describe any real-world situation we know of.
The change in momentum of the book could be described as an impulse due to gravity, but this is consistent with the book having a force of gravity acting on it at every moment during its fall. Again, the impulse tells you the change in momentum, it's always understood that the change in momentum can be explained in terms of forces acting on both objects during the collision. In the case of an elastic collision where none of the objects' linear kinetic energy is lost to heat you can derive the change in momentum from conservation of kinetic energy and conservation of momentum, without ever needing to consider the forces.
But you could analyze the forces during an elastic collision if you wished this pdf has an analysis of forces during collisions of metal spheres , and you'd end up getting the same answer for the change in momentum as was arrived at just using conservation laws. The force of gravity acting between the Earth and the Moon will be in effect for billions of years, until one of the bodies is destroyed. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Learn more. The elusive difference between force and impulse Ask Question.
Asked 6 years, 10 months ago. Active 5 years, 1 month ago. Viewed 10k times. Can you explain why do not refer to the fall of the book as the impulse of gravity? Why if the same short time happens in a collision we call it an impulse? Isn't always a force actually an impulse? But, also when the book falls to the ground because of gravity there is a change of momentum, why is that not impulse?
That is the elusive difference, for me. Improve this question. Add a comment. Active Oldest Votes. Response to response to edit: I'm not sure I fully grasp what you mean regarding the book, but the force of gravity acting on the book does indeed produce an impulse.
Improve this answer. Case B : The same Jumbo egg is released from a 5-meter height; it falls to the ground and stops. The collision time is the same for each case. Which variable is different for these two cases? Which case involves the greatest momentum change? In this question, you will have to compare two collisions of an egg with the ground. In one case, the egg collides is dropped from a 5-meter height.
In the other case, the egg is dropped from a 1-meter height. Here's how to think about the physics of these collisions:. First you must determine what the variable is. It is either the velocity change Delta V , the collision or contact time, or the mass of the eggs.
The question tells you the two eggs have the same mass and that the collision time is the same for each. So by careful reading and the process of elimination, the variable in these collisions is the velocity change. The usual motion of a car is easy to observe with an ordinary video camera. A collision between solid objects is not so simple. Knowing the mass of the ball we can calculate the impulse.
But it takes a very high speed camera to determine how long the ball was in contact with the bat. We can calculate the impulse, and with this information make some good approximation of the average and maximum force. How does force differ from impulse? Paul N. Sep 24, Related questions Question cf2dd. What does force mean?
What are some examples of forces? What is a centrifugal force?