chapter 2—motion and force section 1—describing motion
TRANSCRIPT
Chapter 2—Motion and ForceSection 1—Describing Motion
Motion and Speed
•Motion—occurs when an object changes its position
• *Motion doesn’t always have to be seen to have taken place
•Reference Point-used to determine how far something moves–Ex: mailbox while driving
Relative Motion
•Relative Motion–Not all motion is obvious–Everything is in motion relative to something else•Ex: the Earth is always in motion around the sun, etc.
Distance and Displacement
• Distance—describes how far something has moved– SI base unit to measure distance
is METER– Displacement—the distance and
direction of an object’s change in position from the starting point•See figure 2 on pg. 39
Speed
• Speed-the distance an object travels per unit of time– Ex: miles per hour/ feet per
minute, etc.– Rate—any change over time, so--
– **Speed is a RATE– Equation: Speed = Distance /
Time– (typically measured in
m/s)
Practice Calculating Speed-pg. 42-# 1 and 2
• *Most speeds aren’t constant, they either slow down or speed up
• Average speed-describes speed of motion when speed is changing
(driving on a 3 hr. trip)
• Instantaneous Speed-speed at a given point in time– Ex: speed on a speedometer
Velocity
•Velocity--includes the speed of an object AND the direction of its motion
• *Velocity can change EVEN IF speed remains constant
•Change in Velocity—can be EITHER a change in speed OR in direction of movement
Remember:*To Calculate Velocity, it is the same as calculating speed, but you must also report a DIRECTION-north, south, east, west, etc.
*One example of change in velocity—when a race car at a constant speed is rounding a curve, velocity is changing, due to direction of travel changing
Plate Tectonics
• The motion of the Earth’s crust creates the continental drifting that occurs every year
• Plate Tectonics Theory-Pangea• Plates move so slowly that their
speeds are given in units of centimeters per year.
• Australian plate-1 of fastest—moves north at an average speed of 17 cm./yr and San Andreas Fault (in CA) about 1 cm/yr
Section 2—Acceleration
Acceleration-the rate of change of velocity (velocity = speed w/direction)
When the velocity of an object changes, the object is accelerating
So: Acceleration occurs when an object changes its SPEED, its
DIRECTION or BOTH
Acceleration:
If speed is increasing = positive acceleration (acceleration)
If speed is decreasing = negative acceleration (deceleration)
Ex: horse on a carousel-acceleration due to direction only
Equation for finding Acceleration:
Acceleration = change in velocity / time
ORAcceleration = final velocity – initial
velocity / time(usually reported in m/s/s or m/s^2)
(if motion is in a straight line, (no change in direction, use change in speed to calculate
acceleration)
Amusement Park Acceleration:Wooden and steel roller coaster provide different thrills due to
different materialsWooden-swaying effectSteel-more loops, steep inclines, drops, etc.
Section 3: Motion and Forces
Force: a push or pull that one body exerts on another
*A force can cause the motion of an object to change
ex: tennis racket on a ballex: billiards
Balanced forces: forces that are equal, but in opposite directions *they do NOT change the direction of the forceNET FORCE-when two balanced forces are combined the net force will be zero (if equal but in opposite directions)
Unbalanced forces: forces that are unequal and in opposite directions*the greater force will cause an object to move in that directionNET FORCE: with unbalanced forces, will be the DIFFERENCE BETWEEN the two forces
Inertia: The tendency of an object to resist ay change in its motion*If an object is moving, it will keep moving at the same speed and direction unless an unbalanced force acts on it*Or: velocity of the object remains constant unless a force changes it
Newton’s First Law of Motion: (Also called Law of Inertia)*An object in motion will remain in motion unless acted upon by an outside force*An object at rest will remain at rest unless acted upon by an outside forceEx: what happens in a car crash-pg. 55