# 8th science forces and motion

When two forces act in the same direction
the add together
inertia
the tendency of an object to resist change in its motion is known as
the greater the mass of an boject
the greater its inertia
weight
the force of gravity on a person or object on the surface of a planet is called
one way to increase acceleration is by
decreasing mass
friction
is the force that one surface exerts on another when the two rub against each other
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which of the following is an example of rolling friction
bike tires on the road as you ride
friction
air resistence ia a type of
the law of universal gravitation states that any two objects in the universe, without exception
attract each other
forces can be added together only it they are
acting on the same object
according to the law of conservation of momentum, when two objects collide in the avsence of friction
momentum is not lost
the achievement of lifting a rocket off the ground and into space can be explained by
Newton’s third law
force
in physical science, a push or a pull is called this
velocity
the momentum of an object is in the same direction as its
mass
the amount of matter in an object is called
gravity
the force that pulls falling objects towards Earth is called
According to Newton’s third law of motion, when a hammer strikes and exerts force on a nail, the nail
excerts an equal force back on the hammer
newton
the SI unit for force is the
balanced forces acting on an object
never change the object’s motion
When an object’s distance from another object is changing
ia is in motion
meter
the basic SI unit of length is
time
Speed equals distance divided by
When you know both the speed and direction of an object’s motion, you know the
velocity of the object
time
you can show the motion of an object on a line graph in which you plot distance against
rise
te steepness of a line on a graph is called
Which is an example of deceleration
a car approaching a red light
time
to determin the acceleration reat of an object, you must calculate the change in speed during each unit of
kilometers per hour per hour
if speed is measured in likometers per hour and time is measured in hours, the unit of acceleration is
average speed is
the total distance traveled divided by by the total time
a reference point
a place or object used for comparision to determine if something is in motion is
on a graph showing distance versus time, a horizonal line represents an object that is
not moving at all
If you know the distance an object has traveled in a certain amount of time, you can determine
the speed of the object
acceleration
changing direction is an example of a kind of
15 km/h
if a bicyclist travels 30 kilometers in two hours, her average speed is
the moon accelerates because it is
continuosly changing directions
average speed
If you know a car traveled 30 kilometers in 3 hours. you can find its….
Balanced forces
do not change an object’s motion
the property of matter that resists a change is notion is called
inertia
friction depends on the types of surfaces involved and how
hard the surfaces push together
masee and distance
affect the gravitational attraction between objects
Newton’s third law of motion states that for every action there is an equal by opposite
reaction
a unit of momentum is
kgrm’s
Motion is measured relative to a
reference point
a child riding on a merry-go-round is accelerating because
his direction is changing
The SI unit of acceleration is
the meter per second per second
The overall force on an object after all teh forces are added together is called
the net force
Unbalanced forces action on an object produce a change in the
object’s motion
a measure of an object’s mass
is a measure of the object’s inertia
on newton
is the force required to accelerate 1 kilogram of mass at 1 meter per second per second
A person traveling in a car that stops suddenly keeps moving forward due to
inertia
the downward force acting on an object in free fall is the force of
gravity
a projectile
is an object that is thrown
at the distance between two objects decreases, teh gravitational force between them
increases
According to Newton’s third law of motion
the strength of a reaction force is equal to the strength of the action force.
If the action force of a bat striking a ball accelerates the ball in one direction,
the reaction force accelerates the bat in the opposite direction
friction acts in a direction opposite
to an object’s direction of motion
a change in an object’s position relative to a regerence point is called
motion
the distance traveled by a moving object per unit if time is called
speed
the basic SI unith of lenght is the
meter
the statement that the motion of a hurrican is 20 kilometers per hour in an easterly direction is a description of the hurricane’s
velocity
acceleration is the rate of change in
speed
the motion of a car stopping at a traffic light is an example of
negative acceleration. also called deceleration
the abbreviation of the unit acceleration is
m/s 2
If a car is speeding up,
its initial speed is less than its final speed
If a train traveling at 30 m/s brakes to a stop in 1 minute
its acceleratio is 0.5 m/s2
It two lines appear on the same motion graph
the line with the steeper slope indicates a greater speed.