Forces and Energy Flashcards
What is a resultant force
When a number of different forces act at a point on an object, they add up to a resultant force. This is the single force that has the same effect as all the original forces combined Simply add up the forces acting in a straight line in that direction (if it points in the opposite direction you must take it away)
What are forces?
Pushes and pulls Measured in Newtons
What do forces do?
Cause an acceleration or, Cause a direction change or, Cause a change of shape or All of the above
What happens if the resultant force is zero? Will the object not move, slow down speed up or stay at the same speed?
The object will continue at the same speed, or if it was already stationary it will remain so This is Newton’s first law of motion.
How are force (resultant force) mass and acceleration related?
Force = mass x acceleration This is Newton’s second law
What are forces measured in?
Newtons (N)
What is mass measured in?
kilograms, kg
What is weight measured in?
Newtons, N It is the force due to gravity
What is speed measured in?
meters per second m/s
What is acceleration measured in?
meters per second per second m/s2
What is speed?
A measure of how fast something is moving. It is the distance moved in a certain amount of time.
What is velocity?
Speed is how fast you are moving Velocity is how fast you are moving is a particular direction. It is a VECTOR quantity. Examples 30km/h North
What does the gradient (how steep the line is) of a distance time graph tell you?
The speed the object is moving at The steeper it is the faster it is moving
What is deceleration?
Acceleration in the opposite direction to the motion (negative acceleration)
What is acceleration
Rate at which velocity changes Change in velocity / time
What does the gradient (how steep) of a velocity time graph represent?
Acceleration
What forces act on a car when it is moving?
Resistance, air resistance, driving force You may also have identified , weight and the normal reaction force from the road on the car
What is the resultant force of a car travelling at constant speed?
Zero
By Newton’s First Law if an object is travelling at constant speed there can be no resultant force acting on it. Otherwise it would be accelerating.
The same constant breaking force is used to stop a car; whatever speed it is travelling at to start with.
Explain what happens to the car’s stopping distance for higher speeds.
It will increase
In fact the braking distance goes up x4 when the velocity goes up x2.
What is the total stopping distance of a car made up of?
Thinking distance (reation time)
+
Braking distance
Which factors affect thinking distance
Tired
Drugs
Distractions (playing music, using mobile phone, chatting)
Age
Which factors affect braking distance?
Road conditions (ice, snow rain, type of road)
Condition of the tyres
Condition of the brakes
How much (approximately) does the stopping distance increase when the speed increases from 30mph to 50mph
at 30mph stopping distance is 23m
at 50mph it is 53m
increase is 30m
What is the definition of weight?
Force on a object due to gravity
Weight (N) = Mass (kg) x Gravitation Field Strength (10 N/kg on Earth)
As an objects fall through air which forces will act on it?
Gravity and Air resistance
The faster the object fall the larger the air resistance will become
What is Terminal Velocity?
When the forces on an object, which is falling, reach an equilibrium (air resistance = weight) the object will no longer accelerate and has reached it’s Terminal velocity
As an object falls through the air (or fluid) it experience a resistive force called DRAG
The faster the object falls the larger this force becomes
It will continue to accelerate until the DRAG force is equal to the downward force
The object cannot accelerate now and has reached TERMINAL VELOCITY
How does a parachute reduce a skydiver’s terminal velocity?
Parachute creates a large air resistance (suddenly)
This force is much greater than the weight cause a new resultant force which decelerates the skydiver
As the speed decreases so does the air resistance on the parachute until a new lower terminal velocity is reached
What is the limit of proportionality?
The point beyond which increasing the force will cause a permament deformation. In other words the spring will no longer return to it’s original shape
What is Hooke’s Law?
Force = Sping constant x Extension
F = k x e
Force applied to an object is directly proportional to the extension
What is the definition of work done?
Another way of saying how much energy is transferred
It is measured in Joules
Work done = Force x distance
W = F x d
What is the definition of Power
How much work is done (or energy transferred) in a given time
In other words, a powerful machine can do a lot of work in a short space of time.
Power (W) = work done (J) / time (s)
or
Power (W) = energy transferred (J) / time (s)
It is measured in Watts (W)
What is Gravitational Potential Energy?
The energy an object possesses due to it’s position in the graviational field. In otherwords how far off the ground it is. The higher it is the more energy it possesses
GPE = mass x gravitational field strength x change in height
GPE = m x g x h
What is Kinetic Energy?
The energy an object possesses due only to it’s motion
KE = 1/2 mass x speed2
KE = 1/2 m x v2
What is the law of conservation of energy?
Energy cannot be created or destroyed
It can only be transferred from one type to another
What 2 things does momentum depend upon?
The mass of an object
The velocity of the object (remember that object which move towards each other at the same speed will not have the same velocity as one will be negative)
momentum = mass x velocity
Unit for momentum are
kg m/s
