3.5 Newton’s laws of motion and momentum Flashcards
What is Newton’s First Law of motion?
An object will remain at rest or continue to move with constant velocity unless acted about by a resultant force.
According to Newton’s First Law of motion:
What happens when an object’s velocity changes?
If an object’s velocity changes, then we know that a resultant force must be acting on the object
Remember, velocity also includes direction, so direction can change
“An asteroid moving in deep space will keep moving at a constant velocity”
Why is this the case? Also mention the rule.
Because there is no force acting on it to alter its motion or velocity.
This is part of Newton’s First law of motion
What is Newton’s Third Law of Motion?
These forces are always of the same type, and have the same magnitude but they act on different objects, and in opposite directions.
What is an important feature to note about Newton’s 3rd Law of motion?
The forces acting on the interacting objects are always of the same type.
Examples:
All forces obey Newton’s 3rd law of motion. What can the forces between the interacting objects be explained as?
They can all be explained in terms of the four fundamental forces.
These are the gravitational, electromagnetic, strong nuclear, and weak nuclear forces.
When an object with mass is in motion, and therefore has velocity, it also has _________________
When an object with mass is in motion, and therefore has velocity, it also has momentum
Define momentum
The linear momentum, p, of an object is defined as the product of the object’s mass, m, and its velocity, v.
p = m v
Give the formula for momentum
momentum = mass x velocityp = m v
- The unit for momentum is kgms⁻¹
Explain what type of quantity momentum is
Momentum is a vector quantity as it is the product of mass (a scalar quantity), and velocity (a vector quantity)
As it is a vector quantity, we must consider both direction and magnitude, and the positive and negative signs.
Whad does the principle of conservation of momentum state?
The principle of conservation of momentum states:
For a system of interacting objects, the total momentum in a specified direction remains constant (it is conserved), as long as no external forces act on the system.
______________________________________________
This means that when object collide, the total momentum before the collision is equal to the total momentum after the collision, provided no external forces acts.
Describe a situation where they may be zero momentum
- When a bullet is fired from a gun, the gun recoils backwards, and a bullet also leaves the gun
- Before the gun is fired, there is zero momentum as there is no motion
- After the gun fires, the bullet gains momentum as it has a mass and travels at a high velocity
- The gun also gains momentum, but in the opposite direction, as it has a mass and also recoils at a certain velocity (although much of this force is absorbed by our bodies when we hold the gun)
- As the gun gains momentum in the opposite direction, the momemtum cancels out - as momentum is a vector quantity - and momentum is conserved - there is zero momentum.
What are two things that are conserved in a collision between objects in a closed system?
Momentum and total energy are always conserved in a collision between objects in a closed system
What are the two types of collisions?
- Perfectly Elastic Collisions - where the total kinetic energy is conserved
- Inelastic collisions - where the total kinetic energy is not conserved. For example, in a collision of two cars the kinetic energy could be transformed as the cars crumple and deform.
What is Newton’s Second Law of motion?
The net (or resultant) force acting upon an object is directly proportional to the rate of change of its momentum, and is in the same direction
Write Newton’s Second Law of Motion in an equation
How can we rearrange the momentum formula to make F = m a ?
[Write Q here]
What is impulse?
Impulse is a measure of change in momentum
