1.3 - Dynamics Flashcards
A force is a push or pull which causes the motion of a body. There’re multiple types of forces. Forces are vector quantities (so they have magnitude and direction) and their magnitude measured in
Newtons (N)
What does Newton’s 3rd law state?
If a body A exerts a force (of magnitude F) on body B, the body B will exert a force of equal magnitude but opposite direction (-F) on body A
What does Newton’s 2nd law state?
The rate of change of momentum of a body is directly proportional to the resultant force acting upon it
See NC 5
What does Newton’s 1st law state?
A object will continue with a constant velocity or remain stationary if there is no resultant force acting on it
Momentum, p = mass, m x velocity, v
p = mv
give the units of p
kg m s-1
State the law of conservation of momentum
In a closed system (where no external forces are applied) the total momentum of the system does not change. It is conserved.
In the laboratory, we often investigate momentum changes using riders on air tracks. A rider sits on a cushion of air so that:
There is 0 resultant vertical force (the upward force on the rider due to air pressure is equal and opposite to the downward gravitational force)
There is 0 frictional force on the rider and the force due to air resistance is very low
See NC 1
What is an elastic and an inelastic collision?
Inelastic collision is one in which KE in lost
Elastic collision is one in which no KE is lost
Elastic collisions are more difficult to analyse than inelastic ones because there are 2 unknown velocities. We need to solve simultaneous equations.
See NC 2
Resultant force =
change in p / change in t
See NC 4
When finding the acceleration of an object find its resultant ______ and horizontal forces
vertical
See NC 3
What are the 4 main kind of forces?
Gravitational
Electromagnetic
Strong nuclear force
Weak force
Not all equal and opposite forces are an N3 pair. Why wouldn’t a reaction be a N3 pair?
They act on the same body
The forces are not of the same kind
