Download Physical Earth Science Chapter 10: Motion

Physical Earth Science Chapter 10: Motion
Section 1: Measuring Motion
Observing Motion – an object must be observed in relation to another object;
Stationary object – the object that stays in its place; also called a reference
point or reference frame
1. Distance measures the path taken
2. Displacement is the change of an object’s position
a. Differences between Distance and Displacement
i. Displacement must be a straight line; distance doesn’t have to
be
ii. Displacement must be in a certain direction
(toward/away/North/etc.)
Speed and Velocity
1. Speed measurements involve distance and time
a. Expressed by meters per second (m/s) or km/h
b. Constant speed – when an object covers equal amounts of distance in
equal amounts of time
2. Speed can be studied with graphs and equations
3. Speed can be determined from a distance-time graph
a. Time is plotted on the x-axis (horizontal)
b. Distance is plotted on the y-axis
c. A resting object has a slope of 0
4. Average speed is calculated as distance divided by time
a. Speed = distance/time (v=d/t)
5. Instantaneous speed is the speed at a given point in time
6. Velocity describes both speed and direction
7. Combine velocities to determine resultant velocities
Section 2: Acceleration
Acceleration and Motion
1. Acceleration can be a change in speed
2. Acceleration can also be a change in direction
3. Uniform circular motion is constant acceleration
a. Centripetal acceleration – the acceleration that occurs in uniform
circular motion
Calculating Acceleration – acceleration = (final velocity – initial velocity)/time
Or a = change in velocity/t
1. Acceleration (to speed up) is the rate at which velocity changes
2. Acceleration can be determined from a velocity-time graph
a. Time on x-axis; distance on y-axis
b. Straight line shows constant acceleration – velocity changes by the
same amount over each time interval
Section 3: Motion and Force
Balanced and Unbalanced Forces – net forces (the combination of all forces
acting on an object)
1. Balanced forces do not change motion
2. Unbalanced forces do not cancel completely
a. An object will move in the direction that the greatest force is applied
b. Object that have forces applied that are not opposite each other will
have movement in a different direction
Force of Friction – friction – the unbalanced force that acts against an object’s
direction of motion – occurs b/c surfaces may be rough
1. Friction opposes the applied force
2. Static friction is greater than kinetic friction
a. Static friction – friction between objects at rest
b. Kinetic friction – friction between objects that are in contact during
motion
3. Not all kinetic friction is the same
a. Sliding friction
b. Rolling friction
4. Air resistance also opposes motion
a. Fluid friction – can be minimized by making a surface smooth
b. Streamlining – making an object less resistant to fluid friction
Friction and Motion
1. Harmful friction can be reduced
a. Use lubricant (motor oil, wax, grease) to reduce friction
b. Replace sliding friction with rolling friction (use of the wheel)
c. Make surfaces smoother
2. Helpful friction can be increased
a. Make surfaces rougher – sand on roads
b. Increase force pushing surfaces together – rock on a magazine in the
wind
3. Cars could not move without friction
a. Cars wheels turn and push against the road
b. Road pushes back on the car causing acceleration