92 terms

# Science - Motion/Forces

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Aristotle
He thought that the rate at which an object falls depended on the object's mass.
Galileo
He argued that the mass of an object does not affect the time the object takes to fall to the ground.
Objects fall to the ground at the same rate
because the acceleration due to gravity is the same for all objects.
Acceleration depends on
both force and mass
Acceleration
this is the rate at which velocity changes over time.
All objects accelerate towards Earth at a rate of
9.8 meters per second per second.
9.8 m/s/s/
This means 9.8 meters per second per second.
In the second second an object falls, the downward velocity is
19.6 m/s downward
In the third second an object falls, the downward velocity is
29.4 n/s downward
In the first second an object falls, the downward velocity is
9.8 m/s downward
The equation for change in velocity is
∆v = g × t
In ∆v = g × t, the g stands for
acceleration due to gravity on earth
In ∆v = g × t, the t stands for
the time the object takes to fall.
29.4 m/s
The speed of an object when it hits the ground after a period of 3 seconds.
19.6 m/s
The speed of an object when it hits the ground after a period of 2 seconds.
If an object hits the ground with a velocity of 98 m/s, how long did it take to reach the ground
10 seconds.
If an object hits the ground with a velocity of 49 m/s, how long did it take to reach the ground
5 seconds
air resistance
force that opposes the motion of objects that move through the air
the force of gravity
this pulls down on a falling object
this force pushes up on a falling object
air resistance
net force on a falling object
the force of air resistance subtracted from the force of gravity.
free fall
This occurs only if gravity is pulling down an object with no other forces acting on it. It is usually accompanied by the playing of a Tom Petty song. :)
free fall only occurs where there is
no air
two places there is no air
space and a vacuum. A third place is also potentially inside an 8th graders brain. :)
weight
this is a measure of gravitational force.
terminal velocity
the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity
why is terminal velocity a good thing
because if there was no maximum speed, things like hailstones would destroy everything in their path.
parachute
this increases air resistance and slows one to a safe terminal velocity.
It is impossible for
any object to be weightless anywhere in the universe.
orbiting
when an object moves in a regular path around another object
centripetal force
any force that causes an object to move in a circular path
centripetal means
towards the center
Why does the moon stay in orbit
because the Earth's gravitational force provides a centripetal force on it.
projectile motion
the curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth
hopping grasshopper
The motion of this activity is an example of projectile motion.
leaping frog, water sprayed by a sprinkler, an arrow shot by an archer
These are all examples of projection motion.
horizontal motion
motion that is parallel to the ground
which two forces combine to cause projectile motion
horizontal motion and vertical motion.
vertical motion
motion which is perpendicular to the ground.
a ball dropped without a horizontal push wll
fall straight to the ground
a ball which is given a horizontal push will
fall to the ground with projectile motion
Does gravity affect horizontal motion?
No, it only affects vertical motion.
If a rock at rest falls off a tall cliff and hits the valley below after 3.5 s, what is the rock's velocity when it hits the ground?
34.3 m/s downward
Newton's First Law of Motion
Objects in motion will remain in motion unless acted upon by another force.
unbalanced force
This is what changes the velocity of an object as defined in Newton's First Law.
unbalanced force that acts upon something pushed on the floor to stop it
friction
Objects at rest
tend to stay at rest until an unbalanced force acts upon it.
law of inertia
The other name for Newton's First Law of Motion
inertia
the tendency of an object to resist being moved or, if the object is moving, to resist a change in speed or direction until an outside force acts on the object.
Newton's Second Law of Motion
The acceleration of an object depends on the mass of the object and the amount of force applied.
Newton's Second Law of Motion: Part 1
Acceleration Depends On Mass
Newton's Second Law of Motion: Part 2
Acceleration Depends On Force
Why do newer cars pollute less than older cars?
They have less mass, so it requires less force to move them.
Acceleration will increase when
a larger force is exerted.
F = m × a
The correct formula for Newton's second law of motion.
Newton's second law explains why objects fall to Earth
with the same acceleration.
What is the acceleration of a 3 kg mass if a force of 15 N is used to move the mass? Note: 1 N = 1 kg×m/s
5 m/s
What is the acceleration of a 4 kg mass if a force of 16 N is used to move the mass? Note: 1 N = 1 kg×m/s
4 m/s
What is the acceleration of a 3 kg mass if a force of 18 N is used to move the mass? Note: 1 N = 1 kg×m/s
6 m/s
What is the acceleration of a 2 kg mass if a force of 18 N is used to move the mass? Note: 1 N = 1 kg×m/s
9 m/s
Newton's Third Law of Motion
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.
Swimmer action force
Hands pushing through the water.
Swimmer reaction force
Water pushing on the hands.
For a swimmer, which force pushes them forward
The reaction force.
A force is always exerted by one object
on another object.
Action and reaction forces are a
pair of forces
Space shuttle action and reaction force pairs
Thrusters pushing the exhaust games downward as gases push the shuttle upward with equal force.
Action and reaction forces example
A rabbit's legs exerting a force of Earth with Earth exerting an equal force on the rabbit's legs causing the rabbit to accelerate forward.
Equal and opposite force
whenever an object exerts a force on another object, the second object exerts this...
momentum
a quantity defined as the product of the mass and velocity of an object.
formula for momentum
p = m × v
What is the momentum of a ball with a mass of 120 kg that moves with a velocity of 16 m/s?
19,200 kg m/s
What is the momentum of a ball with a mass of 100 kg that moves with a velocity of 16 m/s?
16,000 kg m/s
What is the momentum of a ball with a mass of 200 kg that moves with a velocity of 16 m/s?
32,000 kg m/s
What is the momentum of a ball with a mass of 200 kg that moves with a velocity of 12 m/s?
24,000 kg m/s
What is the momentum of a ball with a mass of 100 kg that moves with a velocity of 12 m/s?
12,000 kg m/s
What is the momentum of a ball with a mass of 150 kg that moves with a velocity of 12 m/s?
18,000 kg m/s
law of conservation of momentum
this means that anytime objects collide, the total amount of momentum stays the same.
when does the law of conservation of momentum apply
then objects stick together or bounce off each other after they collide.
billiard balls bouncing off one another
This is an example of the law of conservation of momentum
The more momentum an object has.....
the harder it is to stop the object or change its' direction.
If a truck has more mass than a car....
a larger force is needed to stop the truck than the car.
If a fast moving car has a greater velocity than a slow moving car....
a larger force is needed to stop the faster moving car.
Objects sticking together
After this happens, they move as one. the masses of the objects remain the same. The velocity changes. total momentum before and after collision stays the same.
Objects sticking together - examples
When one football player tackles another player or when a dog catches a ball.
Objects bouncing off one another - examples
Bowling balls and pins, billiard balls
Objects bouncing off one another - what is happening
Momentum is transferred from one object to another object.
Objects sticking together - what is happening
The mass of the combined object is equal to the mass of the two objects added together. Together, the one object has a velocity which is different from the velocity of the two individual items.
Conservation of momentum is explained by
Newton's 3rd Law of Motion
When a cue ball hits a billiard ball.......
the cue ball creates the action force, which makes the billiard ball move.
What is the reaction force when a cue ball hits a billiard ball.......
this is the equal but opposite force exerted by the billiard ball on the cue ball. It make the cue ball stop moving.
Momentum is a property of....
moving objects.