Chapter 2—Motion and Force Section 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 –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 OR Acceleration = 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 materials Wooden-swaying effect Steel-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 ball ex: billiards

Balanced forces: forces that are equal, but in opposite directions *they do NOT change the direction of the force NET 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 direction NET 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 force Ex: what happens in a car crash-pg. 55