Transcript Chapter 6 physical science

Chapter 6 physical
science
Forces and motion
Section one
gravity and motion
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In ancient times, Aristotle believed the rate at which an object falls,
was dependant upon the mass of that object.
In the 1500’s Galileo Galilei questioned this and argued mass did
not control the time it took for objects to fall.
Objects fall to the ground at the same rate due to gravity.
All objects accelerate toward the Earth at 9.8 meters per second per
second or 9.8 m/s squared.
For every second an object falls, it accelerates at 9.8 m/s.
Air resistance is the force that opposes motion of objects through
air.
Section 1 page 2
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The amount of air resistance depends upon the size, shape, and speed of
the object.
The more surface area exposed on the object the more air resistance
affects it. For example, a crumpled sheet of paper is affected more than a
flat sheet of paper.
As speed of a falling object increases, air resistance increases until it equals
the downward force of gravity. Then the object reaches terminal velocity
and velocity remains constant.
Terminal velocity is a very good thing during a hailstorm, otherwise the
hailstones might reach a speed of near 350 m/s.
An object can be in free fall only if gravity is the single force acting on the
object. Air resistance must be removed for an object to be in free fall.
Space and a vacuum are the only places objects can be in free fall.
Astronauts float in a spacecraft, because they are in free fall. As the
spacecraft moves forward and free falls toward the Earth, that is known as
orbit.
Section 1 page 3
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Centripetal force causes an object to move in a circular path.
Projectile motion is the curved path an object follows when it is
thrown or propelled near the surface of the Earth. It includes
horizontal motion and vertical motion.
When you throw a ball, you give it horizontal motion, gravity gives it
veridical motion.
You always want to aim above an object to account for the vertical
motion of the object.
Section 2 Newton’s Laws of Motion
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In 1686 Sir Isaac Newton explained the relationship between force
and the motion of an object with his three laws of motion.
Newton’s 1st law of motion states an object at rest remains at rest
and an object in motion remains in motion at constant speed and in
a straight line unless acted upon by an unbalanced force.
Examples of 1st law: a chair remain still on the floor until a force is
applied. When a bumper car strikes another car, the car changes
speed and direction but the driver continues in the same direction at
the same speed until the seat belt stops them.
Friction is a force that affects the 1st law of motion
Section 2 page 2
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The 1st law is often referred to as the law of inertia. Inertia is the
tendancy to resist any change in motion.
An object with a small mass has less inertia than an object with a
large mass.
Newton’s 2nd law of motion states the acceleration of an object
depends on the mass of the object and the amount of force applied.
For example, it is easier to push an empty grocery cart than a fully
loaded grocery cart.
Acceleration can be increased by applying more force to the object.
Newton’s 3rd law of motion states whenever one object exerts a
force on a second object, the second object exerts an equal and
opposite force on the first.
The 3rd law can be thought of as all forces act as pairs. When you
apply a force to an object, the object applies force to you. These are
called action/reaction forces like a swimmer traveling through
water.
Section 3 page 2
Section 3 momentum
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Smaller objects are easier to stop than larger objects due to momentum.
Momentum depends on the object’s mass and velocity.
Momentum (p) is calculated by the formula p = m x v. M = mass and v =
velocity.
When a moving object hits another object, some or all of the momentum is
transferred to the second object. For example when a cue ball strikes
another pool ball, energy is transferred.
When objects collide, they may; 1. stick together or 2. bounce off each
other