Download Josh`s physics kinematics outline

Joshua Lariscy
4th period AP
1/21/11
Kinematics
Coordinate systems
Whenever you decide to start a stopwatch in an experiment or where to
place the ruler, you are defining a coordinate system. The system will
have an origin where both variables in the system have the value of 0.
The system will also consist of one or two axis.
Vectors and Scalars
When a quantity or measurement has both size, called magnitude, and
direction, the quantity can be defined as a vector. Vectors can be
represented by arrows.
Vector examples: displacement, velocity, force, momentum
Vectors must always be connected from the head of one to the tail of
another.
Scalar quantities have a magnitude but have no direction.
Examples: time, temperature
Displacement is a change in position. It is represented by the equation,
d  d f  di
Velocity is a measure of the speed at which an object moves. It is a ratio
of the change in position, or displacement, of an object to the time
interval during which
 the change occurred. This is called average
velocity and is represented by the equation
Joshua Lariscy
4th period AP
1/21/11
v
d d f  di

t
t f  ti
The slope of a position vs. time graph tells you the average velocity of
an object.
Velocity if often measured in meters/second or m/s

Acceleration
If an objects velocity is changing, it is accelerating. If the
velocity is increasing, it is accelerating; decreasing,
decelerating.
The average acceleration of an object is the change in velocity
during a certain time interval divided by that time interval.
Average acceleration is measured in m/s2
The slope of a velocity vs. time graph tells us the acceleration.
Finally, the equation for average acceleration is
v v f  v i
v

t t f  t i
If you know the average acceleration, you can find the final
velocity of an object during a time interval.
v f  v i  a t

If an object moves at a constant acceleration, you can relate it
to its position and velocity with the equation

v f 2  v i 2  2a x
One-Dimensional Motion

Joshua Lariscy
4th period AP
1/21/11
A force is a push or pull exerted on an object. Forces can cause objects
to speed up, slow down, or change direction.
There are two types of forces: contact and field. Contact forces occur
when you directly touch an object. Field are exerted with no contact.
You can represent all of the forces acting on an object by using a free
body diagram.
The forces acting on the cylinder include the force of gravity pushing
down on it, the normal force of the table pushing back on the cylinder,
the applied force pushing on the object from the left, and the frictional
force of the table resisting the object’s movement.
The sum of all the forces acting on an object is called the net force. If
the object is not moving, or if the object is at a constant velocity, the net
force is 0. To describe the object, you say it is in equilibrium.
There are many types of forces that act on objects. Frictional force,
which is created when an object moves against another object, tension,
which is the force exerted by a rope or string, and weight, or force due
to the acceleration of gravity.
Two-Dimensional Motion
Sometimes we deal with problems in two dimensions. The problem
requires adding vectors when they do not point along the straight line
Joshua Lariscy
4th period AP
1/21/11
Vector Algebra
When adding vectors, the vector that represents the sum of the other
vectors is called the resultant. The resultant always points from the tail
of the first vector to the tip of the last vector.
The red vector is the resultant of the two blue vectors.
Because the angle of the vectors is not a right angle, we can use
sin, cosine, and tangent ratios to solve for the resultant
vector. Using a protractor, we can find the angle the two
vectors create.
Vector Components
To solve two dimensional problems, vectors can be broken down into
their components. Every vector has a vertical and a horizontal
component.
Projectile Motion
Joshua Lariscy
4th period AP
1/21/11
Objects that are shot through the air are called projectiles. Each
projectile follows a certain trajectory. If you know the initial thrust
that the object received, you can calculate the trajectory. To calculate
the trajectory, you must break the vector of the projectile into its
horizontal and vertical components.
Remember, when an object travels through the air, its horizontal
velocity remains constant because there is no force acting on it after it is
propelled. Vertically, the force of gravity accelerates the object.
Problems
1.
An airplane drops a crate while flying at a
constant velocity and altitude. Ignoring air resistance, where will
the plane be relative to the crate when the crate hits the ground?
A. Slightly ahead of the crate
C. Directly above the crate
B. Behind the crate
D. Far ahead of the crate
2.
71N
56.7N
25.0
degrees
What is the net force acting on the ring?
45.0 degrees