Motion

In physics… MOTION means a change in the location of a body It is the result of applied force Typically described in terms of velocity, acceleration, displacement, and time. Velocity cannot change unless it is acted upon by a force, as described by Newton's first law. Momentum is directly related to the object's mass and velocity, and the total momentum of all objects in a closed system (one not affected by external forces) does not change with time, as described by the law of conservation of momentum.

Motion is always observed and measured relative to a frame of reference A body which does not move is said to be at rest As there is no absolute reference frame, absolute motion cannot be determined; this is emphasized by the term relative motion. A body which is motionless relative to a given reference frame, moves relative to infinitely many other frames. Thus, everything in the universe is moving. 1

Measuring Motion Motion is measured by distance, using either standard or metric system StandardMetric InchesCentimeters YardsMeters MilesKilometers And now, the metric system in 30 seconds… To convert, move the decimal For example, if you have cm, and want to know how many decameters that is, move the decimal 3 places to the left = decameters KHDMDCM ieeeeei lcctcnl otaeitl arii 2

Calculating Speed Speed = Speed – the distance an object travels in one unit of time Measured in length per unit time, such as meters per second (Meters per second is written as m/s or m/sec) Constant Speed – speed of an object does not change Average Speed – total distance divided by the total time Instantaneous speed – object’s speed at a particular moment in time Velocity – speed in a given direction Distance (d) Time (t)

Graphing Speed When graphing speed, time is put on the X-axis, and distance on the Y-axis Calculate the speed of Student A and Student B from the graph 3

Graphing Speed Student A Travels 1 meter in 1 second S = d/t S = 1 meter/1 second S = 1 m/sec Student B Travels 0.5 meters in 1 second S = d/t S = 0.5 meter/1 second S = 0.5 m/sec 3

Acceleration Acceleration = Final speed (S f ) – Initial speed (S i ) Time (t) Change in speed divided by the time it takes to make that change. Acceleration occurs when an object’s speed increases or decreases. The car’s speed is increasing, acceleration is to the right (acceleration is the same direction of the motion) The car’s speed is decreasing. Acceleration is now to the left (acceleration is in the opposite direction of the car’s motion) Direction of Motion 4

Graphing Acceleration When graphing acceleration, time is put on the X-axis, and speed is now on the Y-axis. Look at this graph. A = positive acceleration (in the same direction as motion) B = constant speed C = negative acceleration (in the opposite direction as motion) 5

Momentum refers to how hard it is to stop an object. An object with greater inertia, once in motion, will require more force to affect its motion. Momentum To calculate momentum, multiply the object’s mass by its velocity P = m ● v Which would be harder to stop?

Vector - a quantity that has magnitude and direction. S N WE 75  North of West 75  Vector direction Vectors Vector magnitude and direction In the example to the left, the force of 316 N represents the magnitude, being applied in a direction of 35  North of East. 6

Time (seconds) Speed (m/sec) Make a graph of acceleration using the data to the left Graphing When making graphs, remember the following: For speed graphs Time goes on X-axis Distance goes on Y-axis For acceleration graphs Time goes on X-axis Speed in meters per second (m/sec) goes on Y-axis

Time (seconds) Speed (m/sec) What is the independent variable? What axis does it go on?

Time (seconds) Speed (m/sec) Time (seconds) How should we divide up the x-axis?

Time (seconds) Speed (m/sec) Time (seconds) What is the dependent variable? What axis does it go on?

Time (seconds) Speed (m/sec) Speed (m/sec) Time (seconds) How should we divide up the y-axis?

Time (seconds) Speed (m/sec) Time (seconds) Speed (m/sec) What else is missing?

Time (seconds) Speed (m/sec) Time (seconds) Speed (m/sec) Acceleration

Review Speed = distance/time (for example, meters/second or km/hr) Velocity = speed in a given direction Acceleration = change in speed / time (units are usually something like meters/second 2

A football player sprinted 40 yards in 5 seconds. What was its speed? V = d/t V = 40 yds / 5 seconds V = 8 yd/sec A baseball was thrown 30 meters and it took the ball 2 seconds to cover the distance. What was the ball’s speed? V = d/t V = 30 meters / 2 seconds V = 15 m/sec

While sky diving, Captain Kirk fell 3000 meters in 10 seconds. What was his speed? V = d/t V = 3000 m / 10 s V = 300 m/s Trying to get home after work, Jane was able to go 4 miles in 4 minutes, the next 2 miles took 6 minutes due to traffic. The final 4 miles took 5 minutes and she was home. What was her average speed? V average = Total distance / total time V average = (4 miles + 2 miles + 4 miles) / (4 mins + 6 mins + 5 mins) V average = 10 miles / 15 minutes V average = 0.67 miles / minute V average = 40 miles/hour

In the final play of the game, the quarterback scrambled 10 yards in 5 seconds, then he ran 10 more yards in 10 seconds, and then he ran the final 15 yards in 5 seconds into the end zone for the win! What was his average speed? V average = Total distance / total time V average = (10 yards + 10 yards + 15 yards) / (5 secs + 10 secs + 5 secs) V average = 35 yards / 20 secs V average = 1.75 yards / sec