6.1 - Further Momentum Flashcards
What is an elastic collision
A collision in which kinetic energy is conserved is called an elastic collision
In general, these are rare. A Newton’s cradle is an example that is nearly perfectly elastic (a tiny amount of energy is lost as sound)
A collision caused by non-contact forces, such as alpha particles being scattered by a nucleus is perfectly elastic
What can elastic collision occur
When forces are non contact
What is an inelastic collision
The total momentum after a collision must be identical to the total momentum prior to it. However, if we calculate the total kinetic energy before and after, we invariably find that the total is reduced by the collision.
Some of the kinetic energy is transferred into other forms such as heat and sound. A collision in which total kinetic energy is not conserved is called an inelastic collision.
What’s important to remember when considering a scenario as inelastic or elastic
Remember that the idea of energy conservation, when considered in order to decide whether a collision is elastic or inelastic, only relates to the kinetic energy. Total energy in all forms must always be conserved !
How can we investigate elastic and inelastic collisions
You can investigate elastic and inelastic collisions in the school laboratory. If you cause head on collisions, and record the mass and velocity of each trolley before and after the collisions, you then calculate the momentum at each stage. This should be conserved.
You can also calculate the kinetic energy before and after the collisions.
Real cars are designed to absorb as much kinetic energy as possible when they crash. This reduces the energy available to cause injury to the passengers. - crumple zones
How can we combine the kinetic energy and momentum equations - what is this useful for?.
E(subscript k) = 1/2mv^2 and v = p/m
Therefore, E(subscript k) = p^2/2m
This formula is particularly useful for dealing with the kinetic energy of subatomic particles travelling at non-relativistic speeds - that is, much slower than the speed of light
How can particle collisions be used
We can use particle collisions in experiments to determine the nature of fundamental particles.
The large hadron collider experiment at CERN uses the conservation of momentum to identify the particles based on calculating the mass. This can be done by colliding particles produced in the experiment with known particles in the detector
If we know the mass and speed of one particle and the speed of the unknown, we can calculate the mass which might correspond to a known particle - so we can identify it.
Define an elastic collision
An elastic collision is a collision in which total kinetic energy is conserved
Define an inelastic collision
An inelastic collision is a collision in which total Kingston energy is not conserved
How do we calculate momentum in 2 dimensions
Momentum should be conserved in each dimension separately. So we resolve vector movements entering a collision into components in each dimension (usually call them the x and y direction) and then calculate following the conservation of momentum in each dimension.
After this, we can recombine component vectors to give us an overall vector after the collision.
How can we investigate impulse, core practical
In an earlier practical, we saw how you can investigate the change in momentum over time for a trolley that is subject to a constant accelerating force. Using the same apparatus, you could again record how different forces acting over different time periods cause the trolley to accelerate to different velocities. From these results, you can calculate the impulse applied in each case, as I = F x triangle t , triangle p = triangle mv
A graph of impulse on the y axis against change in velocity on x axis should give a straight best fit line through the origin. This straight line verifies the impulse equation, and the gradient of it will give the mass of the accelerating trolley and weights.
The book says make sure you have a good understanding of this practical as your understanding of the experimental method may be assessed in your examinations - ay hint hint 😰🤩
What is impulse
The product of a force applied for a certain time (F x triangle t) is known as impulse, this is equal to the change in momentum
Impulse (Ns) = force (N) x time (s) = change in momentum (kgm/s)
Impulse = F x triangle t = triangle p
To stop something moving, we need to remove all of its momentum. This idea allows us to calculate the impulse needed to stop an object moving. If we know how long a force is applied, we could work out the size of that force.
Tell me about deep space collisions
There is an asteroid named Apophis which has a small change of colliding with earth in 2035, 2036 or maybe 2037, and there have been some calls for a mission to crash a spacecraft into Apophis in order to deviate out of harms way. In order to change its momentum and direction.
Tell me about investigating 2D collisions
You can investigate two dimensional collisions in the school laboratory. We can analyse video footage of an objects movement, frame by frame, we can calculate any changes in velocity. With measurement scales in two dimensions,the components of velocity in each dimension can be isolated. Thus, separate calculations can be made in each dimension, in order to verify the conservation of momentum in 2D.
Define impulse
The impulse is force acting for a certain time causing a change in an objects momentum.
Impulse = F x triangle t
