Chapter 3~ Dynamics - Explaining Motion Flashcards
Definitions, key ideas 💡 and formulae
What is Newton’s second law of motion?
The resultant force acting on a body is directly proportional to the rate in change of momentum
The 2 equations for force :
F=ma
F=🔼 p/🔼 t
(p-momentum)
The 2 equations for force :
F=ma
F=🔼 p/🔼 t
(p-momentum)
The mass of an object is 2 things :
- A measure of its inertia
2. It’s ability to resist any change in its motion
If the force is constant, the acceleration is inversely proportional to the…
Mass
So (a is proportional to 1/m)
*inversely means fraction
Define Newton : plus the formula that links
One Newton is the force that will give a 1kg mass an acceleration of 1ms^-2 in the direction of the force.
Formula: 1N =1Kgms^-2
The 6 base units you learn in AS level and their symbols and units :
- Length (x, l, s, etc. ) = metre
- mass (m) = kilogram
- time(t) = second
- electric current (I) =ampere (A)
- thermodynamic temperature (T) = Kelvin
- amount of substance (n) =mol
Definition of a homogeneous equation
When each term in an equation has the same base unit
The 5 multiples, their prefixes and symbols
Kilo (K) 10^3 Mega(M) 10^6 Giga (G) 10^9 Tera (T) 10^12 Peta(P) 10^15
Sub-multiples, prefixes and their symbols
Deci (d) = 10^-1 Centi (c) =10^-2 Milli (m) =10^-3 Micro (u) =10^-6 Nano (n) =10^-9 Pico (p) =10^-12
What is weight?
Weight of an object is a force caused by the Earth’s gravity. It acts vertically down on the object through its centre of gravity
Weight doesn’t affect the rate at which objects falls. Objects that are exactly the same but one is heavier will fall at the same rate. But what does affect the rate then (e.g. Of a feather and a rock)
Air resistance
Definition of inertia :
The reluctance of a body to its change in motion or having its velocity changed
Newton’s first law
An object will remain at rest or in a state of uniform motion unless it is acted on by a resultant force
What is terminal velocity?
It is the maximum velocity of an object when the air resistance is equal to the weight of the object
Forces on an object are balanced when when the resultant force on the object is
Zero
What are viscous forces?
The resistive forces that objects experience when they move through a fluid
What does a fluid refer to?
Liquid or gas
What are the 14main forces?
- Pushes and pulls
- Weight
- Friction
4.drag
5.upthrust
6.contact force
7.tension
8 compression
9.electrostatic
10.magnetic
11.elecromagnetic
12.weak or strong nuclear ⚛ - Electro-weak
14.gravitational
Newton’s third law of motion (2)
When two bodies interact, the forces they exert on each other are equal in magnitude and opposite in direction.
Or
When a body exerts a force on another body then the second body exerts a force back on the first body (called the normal, contact or reaction force) that has the same magnitude, is of the sand type, acts along the same straight line and in acts in the opposite direction as the force exerted by the first body
The two forces that make up a ‘Newton’s third law pair’ have 4 of following characteristics :
- Act on different objects
- equal in magnitude
- Opposite in direction
- the forces are of the same type
Change in momentum is equal to
🔼p= m🔼v
Still must add descriptions of forces
..
Projectiles:
What is a trajectory?
A path followed by a body
If an object is falling what happens to the horizontal and vertical velocity?
Constant horizontal velocity bec there is no force in the horizontal distance.
Increasing vertical velocity due to the force of gravity.
You can use the equations of motion for projectiles as long as there is constant/uniform…. And acts along a…
Acceleration
Straight line (can be a parabola but the values used must be from the straight line distances)
State Newton’s first law
A body will remain at rest or travel with a constant velocity unless it is acted on by a net external force
The change in momentum =
🔼p= m🔼v
What is Friction (also air resistance or drag)?
When 2 bodies are in contact their attractive molecular forces (due to their e-‘s and p+’ s) try to prevent their common surfaces moving relative to each other
What is tension?
The force exerted by a body when it is stretched. It is due to attractive molecular forces.
What is compression?
The force exerted by a body when it is compressed. It is due to repulsive molecular forces.
What is fluid upthrust?
The force exerted by a fluid on a body because of the weight of the fluid that has been displaced by the body.
Archimede’s principle states that the upthrust force is equal to the weight of the fluid displaced
What are electrostatic forces?
Attractive and repulsive forces due to moving electric charges
What is electromagnetic forces?
Attractive and repulsive forces due to bodies being charged.
Contact, friction, tension, compression, fluid upthrust, electrostatic and magnetic forces are all forms of electromagnetic force.
What is weak nuclear forces?
This is the force responsible for nuclear ⚛ decay
What is electro - weak forces ?
It is now thought that both the electromagnetic and weak nuclear ⚛ forces are both forms of this fundamental force
What is strong nuclear ⚛ force?
The force responsible for holding protons and neutrons together within the nucleus. It is one of the fundamental forces
What is gravitational force (9.81ms^-2)?
The force exerted on a body due to its mass. One of the fundamental forces
Weight =
Mass × gravitational force
