P8 Forces In Balance Flashcards
Scalars and vectors
Scalars:
-scalar are quantities that inly have magnitude
E.g mass is a scalar quantity since it is a quantity and no direction
Vector:
-have both magnitude and direvtion
-when describing the velocity of car it is important to mention both speed and direction- 60km per hr in westerly direction
Comparing scalara and vector quantitys-examplesy
Scalar:
Distance
Speed
Mass
Energy
Volume
Density
Temperature
Power
Vector:
Displacement
Velocity
Weight
Force
Acceleration
Momentum
Imagine a car travelling around a roundabout at a constant speed. While it speed is constant, its direction is constantly changing-so its velocity is constantly changing therefore it id accelerating
Representing vectors
-a vector can be represented by using an arrow
Length of the arrow represents the magnitude of vector
The direction of arrow indicates the direction of vector
Forces between objects- contact and non-contact forces (all named forces)r
Force is defined as:
A push or pull that acts on an object due to the interaction with another object
Forces can have an effect on bodies such as:
-can change their speed,direction and shape
Examples are:
-an engine can increase speed of vehicle due to thrust
-a comet’s direction can be affected by gravitational force
-a spring can have its shape changed by force of heavy load
Weight-force of gravity on mass
Electrostatic force-force between 2 charged objects
Thrust-force causing an object to move
air resistance (drag)-friction of air moving an object
Compression-forces that act inward on an object
Upthrust-the force of a fluid pushing an object upwards
Tension-force transmitted through a cable or string when pulled on by forces acting in its opposite ends
Reaction force-a force due to contact between 2 objects
Lift
Contact forces
-a force which acts between objects that are physically touching
Examples:
Friction-a force that opposes motion
Air resistance-type of friction
Tension-a force that pulls 2 objects connected by a length, such as a string or rope
Reaction force- a force that pushes touching objects apart
Also:
Compression
Drag
Lift
What is a non-contact force?
-a force which acts at a distance, without any contact between bodies,due to the action of the field
Examples of non-contact forces:
Gravitational attraction - the attractive force experienced by 2 objects
Electrostatic force-a force experienced by charged objects which can be attractive or repulsive
Magnetic force-a force experienced between magnetic poles that can be attractive or replusive
Equal and opposite forces-newtons third law
Newton’s third law of motion states that when two objects interact with each other, they exert equal and opposite forces on each other.
E.g a boxer who punches a bag with force of 100N experiences and equal and opposite force of 100N from bag
Friction in action
-driving force on a car is force that makes it move (motive or engine force)
-force pushes the car forward as there is friction between the ground and tyre of each drive wheel.
-friction acts where the tyre is in contact with ground
Car moves forward:
-force of friction of the road on the tyre is in forward direction
-force of friction of the tyre on road is in reverse direction
Forces pairs
-when there is an interaction between 2 objects, a force is exerted on each object-known as a force pair
Examples:
-downwards force due to weight of a laptop resting on a desk, desk exerts a normal force back up on the laptop
-the tension exerted along a cable to suspended object is opposed by the force of the weight of the object
Whats newtons first law of motion
States that of the force acting on an object are balanced, the resultant force of an object is zero:
-if the object is at rest it stays stationary
-if the object is moving, it keeps moving with same speed and in same direction
Resultant force
-a resultant force is a single force that describes all of the forces operating on a body
-this single resultant force determines:
The direction in which the object will move and as a result of all forces
The magnitude of the final force experienced by the object
Forces can combine to produce balanced and unbalanced forces
Balanced:
-balanced forces mean that the forces have combined in such a way that they cancel each other out and no resultant force acts on body
E.g the weight of a book on a desk is balanced by the normal force of the desk
As a result no resultant force is experienced by the book, the book and table are equal and balanced
Unbalanced:
-unbalanced forces mean that the forces combine in such a way that they do not cancel out completely and there is resultant force on the object
-if person A pulls with 80N to the left and person B pulls with 100N to the right, the forces do not cancel each other out completely
-resultant force will be 20N to the right
Free body diagram-example of forces
-Tension is the force experienced by a cable,rope, or string when pulled, hung,rotated or supported
Normal contact force:
The force arising when an object rests against another object at a 90 degrees to the plane of contact
-sometimes called reaction force
-force arises from Newton’s third law
Upthrust:
The upward buoyancy force acting on an object when it is in fluid
Free body diagrams
-free diagrams are useful for modelling the forces that act upon an object
-each force is represented as a vector arrow, where each arrow:
Is scaled to the magnitude of the force it represents
Points in the direction that the force acts
Is labelled with the name of the force that it represents
What is the centre of mass and how to find it
The centre of mass of an object is the point at which mass can be thought of as being concentrated
Centre of mass=centre of gravity
Centre mass diagram:
-firstly you need equipment:clamp stand, the shape, pen,cork and plumb bob
-you need to attach cork into a clamp stand firmly at top of clamp stand
-after, attach the shape onto the cork and needle so it hangs of one whole
-next attach the plumb bob onto the cork and needle so it is in front of shape
-draw line on the shape where the plumb bob is showing the centre line and after the changed the angle and do the same thing and the joined lines will show the centre of mass
Work done
-work is done when an object is moved over a distance by a force applied in the direction of its displacement
It is said that the force does work on the object
If a force is applied to an object but dosen’t result in any movement, no work is done
Calculating work done:
-amount of work that is done is related to the size of the force and the distance moved by the object in the direction of the force
Where:
Work done= force x distance moved
W=work done in joules or newton-metres
F=force in Newtons
S= distance in metres
Work done and energy transfer
-whenever any work is done, energy is transferred from one store to another
-mechanical working is an energy transfer pathway
-the amount of energy transferred (joules) is equal to work done (also in joules)
Energy transferred (j)= work done (j)
-if a force acts in the direction that an object is moving, then the object will gain energy
-if the force acts in the opposite direction to the movement then the object will lose energy
Work done and friction
-friction is a force that works in opposition to the motion of an object-slows down the motion of object
-when friction is present,energy is transferred by heating-this the raises the temperature of the object and its surroundings. Work done against the frictional force causes the rise in temperature
-imperfections at the interface between the object and the surface bump into and rub up against each other
-air resistance is a type of fiction thats slows the motion of an object
