4-1: Accelerated Motion
- According to Newton’s 2nd law, a net force acting on
an object causes the object to accelerate in the direction of the force.
- The size of the acceleration depends on the strength
of the force and the mass of the object … F = ma.
- Near Earth’s surface, gravity causes falling objects
to accelerate at the rate of 9.8 m/s2.
- A falling object will speed up to a terminal velocity
and maintain that speed … due to the drag caused by air resistance.
- Ignoring air resistance, all objects accelerate at
the same rate, regardless of mass.
- Air resistance acts in the direction opposite to that
in which the object is moving.
4-2: Projectile and Circular Motion
- Objects thrown or shot through the air are called projectiles.
- All projectiles have both horizontal and vertical velocities.
- If air resistance is ignored, the horizontal velocity
is constant; the vertical velocity, which is affected by gravity, increases.
- When an object moves along a circular path, it is accelerated
toward the center of the circle.
- When an object is influenced only by gravity, it is
said to be in free-fall.
- Objects in free-fall can be considered weightless.
4-3: Sending up Satellites
- Artificial satellites are placed in Earth’s orbit for
communication, weather-monitoring, scientific, and military purposes.
- Rockets are used to carry satellites up to the desired
orbit height and to then give them the proper orbital velocity.
4-4: Action and Reaction
- Forces always act in pairs.
- Newton’s 3rd law says for every action there’s an equal
and opposite reaction.
- The forces in an action-reaction pair are always equal
in size and opposite in direction.
- All moving objects have momentum.
- The momentum of an object is the product of its mass
and velocity … Momentum = mv.
- The total momentum of a set of objects is conserved
(no gain or loss) unless a net force acts on the set. |
