Science Chapter 11 webnotes

Chapter 11, Lesson 1
Position: the location of an object
Motion: a change in position over time
distance (meters, kilometers, feet, and miles)
direction (compass or protractor; units of degrees)
Frame of Reference: group of objects from which you can measure a position or motion.
Speed: how fast an object’s position changes over time
Divide distance by time
I went 65 miles in 1 hour…..I drove 65 miles per hour (mph)……65 divided by 1
I ran 100 meters in 10 seconds. My speed was 10 meters per second (m/s)….100 divided by 10
A speedometer shows your instantaneous speed. (speed at given moment)
If you calculate your speed for an entire trip you would find your average speed.
Velocity: measurement that combines both speed and direction of a moving object
Acceleration: change in velocity over time for an object
To calculate acceleration find speed divided by time
180 m/s divided by 6 s = 30 (m/s)/s
“Acceleration” technically occurs when slowing down as well.
This is denoted by a negative number or we can say the car decelerated.
Momentum: the product of mass multiplied by velocity
Momentum = mass x velocity
4kg x 5 m/s
20 kg m/s
Inertia: the tendency of an object to keep moving in a straight line
The larger the mass of an object, the greater its inertia.
Chapter 11, Lesson 2
Force: any push or pull from one object to another
Newton (N) or pound (lb.) are the units used to measure force
We use arrows to show the direction and strength of forces.
Airplanes have many forces.
Thrust: push or pull forward
Lift: raises into the air
Drag: pull that slows down
Gravity: force that pulls all things together
Friction: the force that opposes the motion of one object moving past another
Depends on the surfaces of the two objects, and how hard they are pushed together
Friction between an object and a surface is called sliding friction.
Balanced forces: a force that acts on an object without changing its motion
Unbalanced forces: a force that causes an object to change motion
Newton’s first law, The Law of Inertia
An object at rest tends to stay at rest, and an object in motion tends to stay in motion unless
acted upon by an unbalanced force.
*A ball not moving will stay still unless some force makes it move.
Newton’s second law, The Law of Acceleration
The unbalanced force on an object is equal to the mass of the object multiplied by its
acceleration. In other words….
Acceleration increases as the force increases,
and it decreases if the object’s mass increases.
*If 2 bike riders are pedaling with the same force, the one with less mass accelerates faster.
Newton’s third law, The Law of Action and Reaction
All forces occur in pairs, and these two forces are equal in strength and opposite in direction.
For every action there is an equal and opposite reaction.
*If a boy jumps on a trampoline, the action force is the boy pushing down on the trampoline….the
reaction force is the trampoline pushing up on the boy.
Lesson 3
Work is the measurement of the energy used to perform a task.
Work on an object changes the amount of energy the object has.
Work = force x distance
Work is usually measured in Newton meters (Nm) or joules (J)
All work involves unbalanced forces causing acceleration.
Movement has to occur in order for work to be done.
Energy is the ability to perform work or to change an object.
Usually measured in units called Joules (J)
Potential Energy: energy that is stored in the position or structure (a spring_
Chemical, nuclear, and magnetic can all be potential energy
Kinetic Energy: energy of a moving object
Heat, electricity, sound, and light can all be kinetic
Law of Conservation of Energy: energy cannot be created or destroyed; it can only change form
Energy changes form whenever it is used to do work.
Kinetic energy often changes to heat energy by friction.
Lesson 4
Simple Machine: a machine that takes one force and changes its direction, distance or strength
Effort: the force you apply to a machine
Load: the object moved by the output
Effort Arm: receives the effort
Resistance arm: delivers the output
Mechanical advantage: the ratio of the effort arm and the resistance arm
Simple machines can decrease the amount of time it takes to do work. (makes it easier)
Lever: a bar that rotates around a pivot point called the fulcrum
Levers are divided into 3 classes.
Wheel & Axle
Inclined Planes (ramp)
Compound Machine: any machine that combines 2 or more simple machines
Efficiency: ratio of input energy to output work (usually a percentage)