P2.2 - Newton’s Laws Flashcards
Newton’s first law
A body will remain stationary or continue moving at a constant velocity unless an external force is applied to it
Newton’s second law
Force - mass x acceleration
Newton’s Third Law
Every action has an equal and opposite reactino
3 qualities of an interaction pair of forces
Each force acts on a different object
The forces are the same size and type
The forces act in opposite directions
Non -contact force
A force produced when objects are in a field. No contact is required for the force to act
Examples of non-contact force
Electrostatic
MAGNETISM
GRAVITY
What is a field
A region where an electrical charge, a magnetic material, or a mass experience a force
Which way to field arrows go
From north to south
Contact force
A force that only acts when objects are in contact
What does normal mean in physics
It means that the force acts at right angles (90 degrees) to the surface
Free body diagram
Shows the forces acting on a SINGLE object. (Arrows have to be proportional all the time)
Ways to word interaction pairs
‘The force of x only and the force of y on x’
E.g. interaction pair for gravity = the force of the human on Earth and the force of Earth on the human
What is resultant (net) force
The force when two or more forces are added together as vectors
how to calculate resultant force if the two angles are at different angle sot one another
Pythagorus’s Theorem - make a triangle
How to resolve a force
If you have one arrow with a value and one angle, use trigonometry to get the other parts. (Look at figure 6 on Page 65 if confused)
Does it require a resultant force to change the motion (speed or direction) of an object
Yes, stimmt
Inertia
A measure of how difficult it is to change an object’s velocity
If speed or direction doesn’t change (meaning they are both constant), what is the resultant force
0
Equilibrium
When all forces acting on an object cancel out and the resultant force is 0
3 things a resultant force can do:
- change the speed of an object
- change the direction of motion of an object
- change both speed and direction of an object
SI Unit of force
Newton’s, N
SI Unit of Mass
kilograms, kg
Terminal velocity
The velocity that a moving object achieves when the resultant force is 0 (forces are balanced)
How to explain the motion of objects when forces are at an angle
Resolve the forces first (trigonometry) to get angles that occur at right angles
How does a rocket accelerate upwards
The force exerted by the gases in the rocket is bigger than the force of the Earth in the rocket - upwards is the direction of the resultant force
Momentum
Mass x velocity
Is momentum a scalar or vector
Vector - take account of direcriob
What is the law of conservation of momentum
In any interaction or collision, the momentum before = the momentum after
Law of conservation of energy
Energy cannot be created or destroyed, only transferred between stores
Elastic collision
Collision where KE is conserved
Inelastic collision
Collision where KE is not conserved, instead some is dissipated as heat and sound. Or when the combined velocity of objects (after they stick together) is not the same as the orginal objects
Work
The transfer of energy.
Commonly done against gravity or friction
Equation for work
Force x distance
SI Unit for work and Energy
Joules, J
How is one J = 1Nm
Split Nm into two parts: N, and m
N = Newton’s =force (m x a)
Hence kgm/s^2
add on m at end (for extra m)
1kgm^2/s^2 = 1J
Power
Rate of energy transfer
4 power equation
P = E(work done)/t
P=V^2/R
P= I^2 x R
P = IV
