3-1: Motion and Speed
- Motion is a change in position of a body.
- Speed is the rate at which a body changes position.
- Instantaneous speed is the speed at a specific moment
in time.
- Constant speed is when the speed does not change.
- Average speed is the ratio of distance traveled to
time and describes motion, even if the speed varies.
- V = ?d/t = (df-di)/t
3-2: Velocity and Acceleration
- Velocity describes the speed and direction of a moving
body.
- Acceleration is the rate of change in velocity (speeding
up or slowing down).
- A = ? v/t = (vf-vi)/t
3-3: A Crash Course in Safety
- Seat belts reduce injuries by limiting impacts and
spreading out the force over more of the body.
- Some people believe that seat belts should be required
by law; other don’t.
3-4: Connecting Motion with Forces
- A force is a push or a pull one body exerts on another.
- Balanced forces acting on a body do not change the
motion of the body.
- Unbalanced forces result in a net force, which always
changes the motion of a body.
- Inertia is the tendency of an object to resist any
change in its motion. This explains why a massive, fast-moving bowling
ball is more difficult to stop than a ping-pong ball at the same speed.
- Newton’s first law says an object’s motion will not
change unless a net force acts on it.
3-5: Gravity
- Gravity (gravitational force) is the force between
2 masses. It’s commonly used to designate the force between an object
and the Earth.
- Gravity causes planets to orbit the sun and people
to remain on Earth’s surface.
- The gravitational force between two objects depends
on their masses and the distance between them. The bigger the mass(es),
the bigger the force. The closer together, the bigger the force.
- Mass is the amount of matter in an object.
- Weight is the force of gravity on a mass. |
