Mechanics
description
Transcript of Mechanics
Mechanics
• Motion Equations and Graphs
• Combining and Resolving Vectors
• Force and Acceleration
• Gravity and Free-Body Diagrams
• Projectile Motion
• Work and Power
• Energy and Energy Conservation
Equations of Motion
For uniform accelerated motion in one dimesion
v = u + at
s = ut + ½at2
v2 = u2 + 2as
Displacement-Time Graphs
Velocity-Time Graphs
Projectile Motion• Independence of vertical and horizontal motion
of a projectile moving freely under gravity.– Vertical Force: Gravity acting downwards– Horizontal Force: Air resistance is usually neglected
Vectors and Scalars
• Scalars only have a magnitude (size)– Mass– Speed– Length– Distance– Energy
• Vectors have a magnitude and a direction– Force– Velocity– Acceleration– Displacement– Field strength
Changing the Subject of a Formula
SOH CAH TOA
Pythagoras Theorem
Resolving Vectors• Resolve a vector into two components at
right angles to each other by drawing and by calculation.
Combining Vectors• Combine two coplanar vectors at any
angle to each other by drawing, and at right angles to each other by calculation
Free-Body Force Diagrams• Draw and interpret free-body diagrams to
represent forces on a particle or on an extended but rigid body, using the concept of centre of gravity of an extended body
Centre of Gravity• The centre of gravity of an object is the
single point that you can consider the whole weight to act through
Newton’s First Law of Motion
– A body will either stay at rest or move with constant velocity unless acted upon by an external force.
Newton’s Second Law of Motion
• F=ma
• The more force the more acceleration
• The more mass, the less acceleration
• Force is directly proportional to acceleration
• Mass is inversely proportional to acceleration
Gravitational Field Strength
• Use the expressions for gravitational field strength g=F/m and weight W=mg
• Gravitational field strength has the units N/kg. On the Earth’s surface this value is 9.8 N/kg which is the same as acceleration due to gravity near the Earth’s surface
Newton’s Third Law of Motion• If an object A exerts a force on object B, then
object B exerts an equal but opposite force on object A
• If you push against a wall, the wall will push back against you, just as hard.
Newton’s Third Law of Motion• Identify pair of forces constituting an
interaction between two bodies.
Kinetic Energy (KE)• The Energy an object has when it’s moving.
Gravitational Potential Energy (GPE)
• The Energy something gains if you lift it up
Conservation of Energy• Work is done to lift an object up. This gives the object
gravitational potential energy. When the object falls back to earth the GPE gets converted almost completely to KE.
Work• W=Fs• Be able to do calculations when the force
is not along the line of motion
Power• Calculate power from the rate at which
work is done or energy transferred.
Applications of Mechanics
• Understand some applications of mechanics, for example to safety or to sports