8th grade science 2nd semester exam

Question Answer
Define motion. Distance from one object to another is changing.
Define reference point. Place/object used for a comparison to determine if something is moving.
Give 3 exemples of reference points. Tree, sign, building
Define and be able to give examples of relative motion 1. Motion that depends on the reference point 2. cars or airplanes on a runway
Be able to compare relative motion from different perspective like skydivers on page 310 Review page 310 in text book
What is the SI unit for distance(length) Meters(m) or centimeters(cm)
What does a centi mean? one hundredth
What does a milli mean? one thousandth
How many centimeters are in a meter stick? 100 cm
Define Speed Distance traveled per unit of time
What is the difference between average speed instantaneous speed? Average speed,
instantaneous Speed -rate in which an object is moving at a given time
What is Velocity? Speed in a given direction;need to know speed and direction
What units are used for velocity SI Unit;meter per second and direction
Define vector and give an example Measurement that includes both magnitude and direction example: Velocity
What does slope represent How fast one variable in relation to the other variable or rate of change
How do you calculate slope? slope = rise/run
If the slope of a straight line is constant the the speed of the object is fast, steady, speed
If the slope of a straight line is zero then the speed of the object is stationary
If the slope of a straight line curved, then the speed of the object is getting faster
define acceleration rate at which velocity changes
List 3 ways to accelerate 1. Increase speed 2. decrease speed 3. changing direction
What is deceleration? An object as it begins to slow down, negative acceleration
What are the units for acceleration(of an object moving in a straight line) ? SI Units=meters per second per second or m/s^2
Be able to explain acceleration . For example what does 8 m/s^2 mean?(see page 322 for text and diagram. ) Objects speed increases by 8 m/s every second
Explain the difference between zero speed and zero acceleration zero speed – there is no motion
zero acceleration – there is no change in velocity
Define Force push or pull
What is SI unit for force Newton (N)
Is Force a vector ? Yes

What is net force? Combination of all forces acting on an object
How can you find the net force of two forces acting in the same direction? in opposite direction? 1.Sum of the two individual forces 2. Difference between two individual forces
Can you distinguish between balanced and unbalanced forces? Balanced-equal forces acting on one object in the opposite direction Unbalanced – causes a change in objects motion
UnBalanced forces can cause an object to do what 3 things? 1. Start moving 2. stop moving 3. Change direction
Unbalanced forces on an object always result in what ? change an objects movement
Do balanced forces acting on an object change the objects movement? No, equal forces are exerted the net force is zero
friction is a force caused by what? Forces that two surfaces exert on each other
The strength of friction depends on what two things? 1. how hard the surfaces push together and 2. types of surfaces involved
friction always acts in what direction? a direction opposite to the direction of the objects motion.
list four kinds of friction and give examples of each. 1 static-sliding a desk 2 sliding- cars brakes 3 rolling- skateboard
what factors affect the friction between two surfaces? 1 how hard they are pushing against each other
2 what type of surface (how smooth)
define gravity force that pulls objects towards each other
what are factors affect gravitational attractions 1 mass 2 distance
define law of universal gravitational. force of gravity acts between all objects in the universe
what is mass and what is weight? be able to distinguish between them. mass-amount of matter in an object
weight-measure of gravitational force exerted on an object ex scales
what are the units for mass and the units for weight? why aren't they the same? mass -kilogram mass is not effected by gravitational force
weight -pounds
be able to explain why your weight on the moon and your weight on the earth are different. wight less on moon because moon's mass is only a fraction of the earth's
according to our scientific definition, what is free fall? when the only force acting on an object is gravity
when are object on earth in free fall? when an object falls
define acceleration due to gravity on earth. the further an object falls its velocity increases
what is the value for acceleration due to the gravity on earth 9.8 meters per second sqaured
How is acceleration due to gravity abbreviated g
what terminal velocity? Can a sky diver have terminal velocity Force of air resistance equals the weight of an object, yes
state Newtons first law of motion an object at rest will remain at rest and an object moving at constant velocity will remain at a constant velocity unless acted upon by unbalanced force.
what are two unbalanced forces on earth that are always unbalanced gravity and friction
what is inertia on what property does inertia depend tendency of an object to resist a change in momentum. mass
why is the first law of motion sometimes called the law of inertia to stop inertia an unbalanced force must be applied
state Newton's 2nd law of motion acceleration depend on the object mass and on net force acting on the object.
what if the formula for force acceleration equals net force over mass
what other units comprise a newton kg(m/s2)
state newtons third law for every action there is an equal but opposite reaction
when given a scenario be able to identify an action force and reaction force ex. hitting a volleyball
Define momentum quantity of motion of a moving body measured by calculting the bodies mass and velocity
What are units for momentum kilograms and meters per second
What does the law of conservation of momentum state? in the absence of outside forces, the total momentum of objects that interact does not change.
Since momentum is conserved, it is never lost but can be transferred
Explain how rockets lift off using Newton's 3rd law. what is the action force? what is the reaction force? exhaust gases push downward at high velocity rocket's exhaust gases push downwards rocket rises and gases push upwards on rocket.
define satellite object that orbits another object in space
what is the SI unit for pressure? pascal
what is a fluid and what causes fluid pressure? fluid:material that can easily flow;caused by individual partials in a fluid.
what is atmospheric pressure and what causes it? weight of the air pushing down; caused by gravity
what happens to atmospheric pressure as elevation increases? as elevation decreases? decreases increases
what is water pressure and what causes it? water pushing down on you; gravity
what happens to water pressure as depth increase? as depth decreases increases decreases
what is buoyant force? upward force
what is buoyancy? ability to float it acts in the direction opposite to gravity
what does archimedes principle state? buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces
use archimedes principle to explain how a ship floats. it displaces the same amour of fluid equal to the weight of the object
Define Density mass per unit of volume
what does paschals principal state when force is applied to a confined fluid the change in pressure is transferred eqully parts of the fluid
what are some examples of paschal's prinicples in everyday life brakes, barber chair, hydolic life
how does a hydraulic system work multiplies force by applying force to a small area

what are some examples of thing that use hydraulics dump truck, backhoes, screw plows
what is the definition of work exert force on an object causing the object to move
what are the units for work joules
what two things does work depend on force and distance
energy makes work easier by changing the amount of energy, distance and direction
the force you apply to the machine is the input force
the force the machine applies to the object output force
the force that you apply over the distance is input work
the force the machine applies over distance output work
in real life output work is less than input work
define energy ability to work or cause change
what the si units for energy joules
KE kinetic energy depends on what two things mass and velocity
which has a greater effect mass or velocity velocity because its squared doubling velocity will quadruple its kenitic energy
PE potential energy) is due to an objects position and shape
gpe (gravitational potential energy) weight and height
GPE depends on two things an objects weight and height
what is the elasticity of PE giving and example potential associates with objects that can be stressed or compressed, bow strings
what does it mean for energy to be transformed when one energy form is transformed into another energy form.
give some examples of energy transformation toaster oven>eletrical energy to thermal energy
strike a match > mechanical to thermal to electro magnetic energy
what is the law of conservation of energy when one form of energy is transferred to another form of energy
no energy is destroyed in the process
what does Einstein have to do with law of conservation of energy he discovered that matter can be transferred to energy therefore in some situations energy is not conserved
waves disturbance that transfers energy from place to place
medium material through which a wave travels
chemical wave waves that require a medium from which to travel
vibrations repeated back and forth or up or down motion
transverse wave waves that wave that move through medium at right angles
longitudinal waves waves that move medium parallel to the way it travels
standing wave wave appear not to move really two waves are pushing through each other
wave length this is between to cooresponding parts of a waves
amplitude max distance the medium carries away the wave from the rest position
frequency number of complete waves past a point in a certain amount of time
crest high part of transfer waves
trough low part of a transfer wave
compression in longitudinal wave they are part of the medium are close together
refraction part of the medium that are spread out
node points of zero amplitude on a standing wave
how do you find the amplitude of a transverse wave measure the distance from the rest to crest of the wave.
how do you find the amplitude of a longitude wave measure how compressed or refracted the medium becomes
refraction occurs when a wave strikes a surface and cannot pass through