Transcript Semester 1 Review

Semester 1 Review
The story so far…
Basic definitions
• Scalar – a quantity of magnitude only, no direction.
• Vector – a quantity with magnitude and direction.
Vector algebra:
• Position is the location of the object compared to a “zero” location.
• Distance is how far something has moved.
• Displacement is how far something moved from a particular position.
Constant velocity – Units: m/s
• An object that changes its position by the same amount every time
interval.
• Speed is how fast something is moving
• Velocity is how fast something is moving with a direction (usually +
means right or up, and – means left or down)
Constant velocity equations
These equations can only be used when on object is moving with
constant velocity.
∆𝑥
𝑣=
∆𝑡
𝑥 = 𝑥0 + 𝑣𝑡
The slope of the position vs. time graph gives the velocity
Newton’s First Law – the Law of Inertia
• An object in motion or at rest will remain in motion in a straight line
at constant speed or at rest, unless a net external force acts upon it.
• In other words, the velocity of an object will remain constant unless a
net external force acts on it.
• Forces are balanced when objects have constant velocities.
𝐹𝑛𝑒𝑡 = 0
Inertia is a property of matter that causes it to resist changes in its
motion. This property is directly proportional to the mass of the object.
Newton’s Third Law – Balanced Forces
• If object A acts on object B such that they do not accelerate, the then
force of object A on object B is equal on magnitude and opposite in
direction to the force that object B exerts on object A.
𝐹𝐴→𝐵 = −𝐹𝐵→𝐴
The action force is equal and opposite to the reaction force.
Breaking vectors into components
• Vectors are usually broken into x and y components which are treated
separately.
Constant acceleration – Units: m/s2
• When the velocity of an object changes by the same amount per unit
time.
• Acceleration is a change in velocity (speed and/or direction)
• speed up, slow down, or turn
Constant acceleration equations
These equations can only be used when an object is accelerating
uniformly.
The slope of
The area under
∆𝑣
the velocitythe velocity𝑎=
time graph
time graph
∆𝑡
𝑣 = 𝑣0 + 𝑎𝑡
gives the
gives the
acceleration.
1 2
displacement.
∆𝑥 = 𝑎𝑡 + 𝑣0 𝑡
2
𝑣 2 = 𝑣0 2 + 2𝑎∆𝑥
Newton’s Second Law
• The net force acting on an object is equal to the
mass of the object times it’s acceleration.
𝐹𝑛𝑒𝑡 = 𝑚𝑎
There is an extra amount of force in one
direction that causes the object to accelerate in
that direction.
The Big Ideas
Types of Forces – Units: Newtons
• Weight – the force of gravity acting on mass
• Applied – force applied by another object or person
• Friction: (f = µ N)
• Static – stationary, rolling
• Kinetic – moving, sliding
• Drag – friction due to a fluid
• Reaction:
• Normal – reaction force due to contact with a surface
• Buoyant – reaction force due to contact with a fluid
Impulse and momentum
• Momentum is inertia in motion: p=mv
• Units: Kg m/s
• Impulse is a change in momentum over some time interval. Originally,
Newton’s second law was expressed in terms of momentum.
𝐽 = ∆𝑝 = 𝑚∆𝑣
∆𝑝
𝐹𝑛𝑒𝑡 =
∆𝑡
Momentum is conserved in collisions.
Energy – Units: Joules
• Kinetic energy –the energy of motion. (𝐸𝐾 =
1
𝑚𝑣 2 )
2
• Gravitational potential energy – energy stored
due to position above some zero position.
𝐸𝑃 = 𝑚𝑔ℎ = 𝑃𝐸 = 𝑔𝑦𝑚
• Elastic potential energy – energy stored due the
stretching or compressing of an elastic object
1
(reversible deformation). (𝐸𝐸 = 𝑘𝑥 2 )
2
Kinetic energy is conserved in elastic collisions (when
things bounce off each other), but not in inelastic collision
(when things stick together).
Work & Power
• Work is a method of energy transfer – when a force is applied and the
object is displaced. Units: Joules
𝑊 = 𝐹 ∆𝑥 𝑐𝑜𝑠𝜃
• Power is the rate at with work is done (the rate at which energy is
transferred). Units: Watts
𝑊 ∆𝐸
𝑃=
=
∆𝑡 ∆𝑡
Circular Motion
• Angular displacement (s)
• Arc length
• Angular velocity (ω)
• Velocity perpendicular to
circle.
• Acceleration toward
center (centripetal)
𝑣2
𝑎=
𝑟