Newton's Laws Flashcards
What are Free-Body Diagrams
Shows all forces acting on body/object
Used to calculate net force
What is Force
Push or pull on an object
Newtons, Vector quantity
Force directly on body = Contact Force
Force acting on body at a distance = Non-Contact Force
What is net force
Sum of all forces acting on object
What is Newton’s 1st Law
“An object will continue to move with a constant velocity unless external, unbalanced force acts on it”
At rest = Stays at rest, Moving = Continues moving at same magnitude & direction
What is Law of Inertia
Object’s tendency to resist a change in motion
Inertia increases as mass increases
- As harder to start moving if stationary
- Harder to stop moving if moving
- Harder to change direction if moving
What is Newton’s 2nd Law
“An external force applied, object’s motion will change either magnitude/direction and acceleration of object directly proportional to net force on object, inversely proportional to mass of an object”
What is the Force Due to Gravity Dependent on
Larger mass = Larger force due to gravity (Weight)
Mass is directly proportional to gravitational force
What is the Acceleration of Object Dependent on
Net Force acting on object, which is directly proportional to acceleration
Mass of object, which is inversely proportional to acceleration
So Net Force = Mass * Acceleration
What is Newton’s Third Law
“For every action there is an equal and opposite reaction”
Forces always in pairs, where the force pair acts on different objects, and can never be added together
Objects A & B interact, they exert forces on each other
What is Normal Force
Force that counteracts acceleration due to gravity
Not a pair of forces in Newton’s Third Law, as acts on same object
What is weight
Force due to something’s mass acting on an object
Vector quantity, Symbol W
What is mass
Amount of matter in an object
Not affected by environment
What is Relationship Between Mass and Inertia
Greater mass = Greater force needed to accelerate = Greater inertia
Therefore mass directly proportional to inertia
What is Apparent Weight
Reaction force due to acceleration due to gravity acting on an object
Force that counteracts gravity
What is Experience of Weight
Object beneath you accelerating up = Apparent weight increased, gravity feels stronger
Object beneath you accelerating down = Apparent weight decreased, gravity feels weaker
What is Momentum
The product of an object’s mass and velocity
If object moving, it has momentum
Vector quantity
What is Momentum Dependent On
How much stuff moving (Mass)
How fast stuff moving (Velocity)
Therefore momentum = mass * velocity
What is Conservation of Momentum
If no external force acting on system, sum of momentum of objects in system before collision in given direction = Sum of momentum of objects in system after collision in given direction
Therefore Sum of momentum before = Sum of momentum after
What Does Seatbelt Do in Motorcycle Safety
Newton’s First Law
Seatbelts lock in severe deceleration, opposing the passenger’s motion
- Is the unbalanced force that acts on the person to decelerate it
Decreases risk of fatality by 50%
What Does Safety Barriers Do in Motorcycle Safety
Stop out-of-control vehicles from running off-road, or travelling into path of other traffic
Newton’s First Law, where it is the unbalanced force that creates a change in motion, significantly decelerating the car to a stop in little time
Newton’s Second Law, where the force needs to be large, as a car weighs a lot and is moving fast, so has a large net force
The barrier withstands large forces, allowing it to provide a normal force back to the vehicles to stop their motion, is very damaging to vehicle, but prevents widespread harm
What Does Airbag Do In Motorcycle Safety
Inflates within few ms of collision
Newton’s First Law, where the driver continues to move towards dashboard due to inertia, the driver continues into airbag, where the airbag starts deflating to ensure that the body slows down over longer time, increasing contact time between head and dashboard
Increased time means less force applied for the same change in momentum to driver
What Does Helmet Do In Motorcycle Safety
Spreads energy of collision over greater area
Newton’s First Law, where motorist will continue moving after crash due to inertia, where the driver will fly off the motorcycle
The outer layer is made from crushable foam, which increases contact time between head and the ground, this increased time means less force applied for same change in momentum to driver
What Do Crumple Zones Do In Motorcycle Safety
Large distance between driver and front of vehicle
Newton’s First Law, where the cars will continue moving towards eachother due to inertia until fully stopped due to unbalanced forces
The large distance increases time period of which the crash takes place, where this increased time means less force applied for same change in momentum to driver
What is Energy
The ability to do work
Symbol E, Joules
What is Conservation of Energy
“Energy cannot be created or destroyed, it can only be transferred or transformed”
Transfer: Transfer energy from 1 object to another
Transform: Transform energy from one type to another
Generally, when Potential Energy decreases = Kinetic Energy increases
What is Power
The rate at which work is done
Force applied to object to keep it moving over time
What is Potential Energy
Position of objects relative to one another
What is Gravitational Potential Energy
Energy due to position above ground / height
Work done against gravitational field
Calculated relative to zero Ep reference level, where point is kept consistent throughout
What is Kinetic Energy
Energy due to motion
Work done = Change in Kinetic Energy
If object is moving, it has Kinetic Energy
What Happens to Kinetic Energy During Inelastic Collisions
Kinetic Energy not conserved, converted to waste forms
What Happens to Kinetic Energy During Elastic Collisions
Kinetic Energy conserved, no waste energy
Kinetic Energy before = Kinetic Energy after
What is Mechanical Energy
Sum of Potential Energy and Kinetic Energy
What is Instantaneous Kinetic Energy or Potential Energy
How much kinetic energy or potential energy an object has at certain point in time
How is Mechanical Energy Lost
When transferred to waste forms (Heat, Sound, Etc.)
Still Kinetic Energy, but not the motion Kinetic Energy
What is Efficiency
Measure of amount of useful energy we get out of a transfer or transformation
What Energies Do Moving Objects Have
Moving objects have both Potential Energy and Kinetic Energy
What is Work
The energy change in object
Done when force causes the object to be displaced, where energy is transferred or transformed
If positive = Energy gained
If negative = Energy lost
What is Relationship of Friction and Work
No friction = All work transformed to Kinetic Energy, box has higher velocity than before
Some Friction = Some work done transformed to sound/head, the rest Kinetic Energy
A lot of Friction = Box moves at constant velocity, Kinetic Energy doesn’t change as all work becomes heat/sound (Waste)
Therefore changing displacement of body dependent on overcoming friction
How To Calculate Work & Displacement At Angle
Find horizontal component of force, as this contributes to work
