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Mechanics

AS91171 - 2.4

Forces A push or a pull measured in Newtons. A vector quantity.
Net Force When forces are balanced there is no net force (speed will remain constant or object will be stationary). When they are unbalanced the object will accelerate or decelerate.
Friction/Drag A force occuring when two objects move against one another or trhough a fluid. Can appose movement, is increased by making surfaces rougher or by pressing them together and is decreased by lubrication.
Scalars Measurements will magnitude only (distance & speed).
Vectors Measurements with both magnitude and direction (displacment, velocity & acceleration).
Distance/Time Graphs Direction isnt consider, distance cannot decrease and the slope gives speed.
Slope of Distance/Time Graphs Gives speed, the steeper the gradient the faster the object, curved lines mean acceleration or deceleration.
Displacement/ Time Graphs Direction is important, displacement may increase, decrease or remain the same, gradient gives velocity (+ve means forward movement, -ve means backward movement).
Speed/Time Graphs No direction, all date points are positive, the line is always above x-axis, gradient shows acceleration and area under the curve shows direction.
Velocity/Time Graphs Shows direction, data points above x-axis show forward motion, data points below show backward motion. Gradient give acceleration and area between graph line and x-axis gives displacement.
Acceleration/Time Graphs Change in direction of an object in motion is shown.
Adding Vectors Trig may have to be used, vectors are shown with arrows.
Vector Subtraction Used to find the difference between final and inital velocity - draw vector arrow in opposite direction to find quantity.
Relative Velocity Movement of 2+ objects, subtract the velocity of your object from the ‘other object’ to show overall relative velocity.
Vertical Motion under Gravity Air friction is disregarded, gravity is acceleration/deceleration.
Object's in Free Fall Objects under the influence of gravity.
Objects Falling Only Acceleration due to gravity is positive.
Objects Thrown Up then Fall Down Acceleration due to gravity is negative.
Horizontal Projectile Motion Objects are at angles to surface and move along symmetrical curved paths, air friction and acceleration is disgrearded.
Speed of Objects in Horizontal Projectile Motion Initial speed = final speed, constant horizontal velcotiy while accelerating downwards, vertical velocity decreases when object moves upwards and increases when moved downwards, vertical velocity = 0 at peak of parabola due to pure horizontal velocity.
Terminal Velocity Rate at which an object falls, determined by gravity, time and friction.
Vertical Projectile Motion Acceleration is considered.
Hooke's Law F = -kx, negative sign represents the spring trying to return to equilibrium position, spring constant (k) is the stiffness of the spring (a large value is a spring that is hard to strech or compress).
Newton's First Law of Motion ‘An object at rest will remain at rest unless acted on by an unbalanced force’.
Newton's Second Law of Motion ‘If an object with mass is acted on by a force it will accelerate’.
Newton's Third Law of Motion 'For every action there us an equal and opposite reaction’.
Forces Acting at Angles According to Newton’s second law, if the object is accelerating horizontally, then the net force must be horizontal.
Centripetal Acceleration Direction and velocity are constantly changing, object is constantly accelerating towards the centre while maintaining a constant speed.
Centripetal Vector Diagram Velocity at any instant is tangent to the circle. vector triangles are utilised - vf is drawn first, then vi is drawn backwards and Δv is used to finish the circle. Vector subtraction shows a change in velocity that points to the centre of the circle.
Centripetal Force Caused by the force keeping the object in a circular motion.
Centrifugal Force Not a real force, the outward senstation when turning corners, explained by newtons first law and related to momentum. Objects will only turn if there is an unbalanced force with enough friction.
Period Symbol - T, measured in seconds. The amount of time it takes for something to happen.
Frequency Symbol - f, measured in Hz. How many times something happens in one second.
Torque Angular or turning force. Related to the size of the linear force and perpendicular distance if the force from the fulcrum or pivot point (fulcrum). Symbol - τ and measure in (N m).
Equilibrium When all forces are balanced.
A Couple Pair of equal but opposite forces acting independently of one another, causes the object to rotate. The rotation of a couple is midway between them.
Centre of Mass Where there is no net torque due to weight, symmentrical objects will have a centre of mass in the middle of them. An object's mass will create a torque if a fulcrum is not placed at the centre of mass.
Fulcrum ‘Point against which a lever turns or is supported’.
Angled Support Forces The principle of balanced torques can be used to find the tension force in angled supports. For a torque to exist the distance and force must be perpendicular.
Kinetic Energy Energy an object possesses due to its motion.
Gravitational Energy The energy stored in an object due to its height above ground.
Elastic Energy Energy an object posses in a strech or compressed spring or elastic.
The Conservation of Energy Energy cannot be created or destroyed, only transformed or transferred.
Energy in Isolated Systems Will remain constant due to freedim from external forces.
Energy in Dynamic Systems Energy loss will be definite due to resistance or frictional losses.
Work The ability to transfer energy. If an object us moved perpendicular to the force then no work is done by the force on that object.
Power The rate of doing work or how much energy is transformed or transferred per second.
Momentum The resultant of mass and velocity or 'mass in motion'. Measure of difficulty stopping an object in motion. Symbol - p, units kg m s^{-1}.
Impulse The objects cahnge in momentum, the time taken to chnge and the force creating the momentum change. The measure for how long a force is placed on an object.
Conservation of Momentum “The total linear momentum of an isolated system remains constant in magnitude and direction unless acted upon by an external net force".
Conservation of Momentum - Sums of Momentum The sum of the initial momentum is equal to the sum of their final momentums.
Elastic and Inelatic Collisions Momentum is always conserved.
Elastic Collisions Ek before and after collision is conserved.
Inelastic Collisions Ek is greater before collision.
Momentum in Two Dimensions Use conservation of momentum because there has been no impulse/external force acting on the system. In an isloated system there is no momentum change.
Created by: hucklefruitfinn
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