Laws of Motion 2 nd Law of Motion

Laws of Motion 2 nd Law of Motion l l l describes a change in the motion of an object when force is applied change depends on l l l strength of force mass of object’s force = mass x acceleration more mass = harder to change more inertia = harder to change

Laws of Motion 2 nd Law of Motion l a change in motion only occurs if a net force is exerted on an object net force changes the velocity of the object net force causes acceleration of the object l l l l change in speed (speed up or slow down) change in direction change in inertia (stop or start) direction of change = direction of force

Speed l l refers to how fast an object moves to determine speed, need to know: l l l distance an object moves amount of time needed to travel that distance speed = distance time an average - most objects don’t travel at a constant speed to graph l l label time on the x-axis label distance on the y-axis

Velocity l speed of an object in a particular direction l speed plus direction l changes when speed or direction changes l Examples: l l 5 mph North 4 mph South

Velocity vs. Speed l Velocity must include a reference direction. Which statement is correct? A) An airplane’s velocity is 600 km/h. B) An airplane’s velocity is 600 km/h south. l An objects velocity is constant only if its speed and direction don’t change.

Average Speed Problems 1) Kira jogs to a store 72 m away in a time of 36 s. What is Kira’s average speed? 2) If you travel 7. 5 km and walk for 1. 5 h, what is your average speed? 3) An airplane traveling from San Francisco to Chicago travels 1, 260 km in 3. 5 h. What is the airplane’s average speed?

Interpret the Graph Below: The graph shows an object which is not moving (at rest). The distance stays the same as time goes by because it is not moving.

Interpret the Graph Below: The graph shows that the object’s distance increases as time passes. The object is moving and so it has velocity (speed with direction). The straight line shows it is a constant (not changing).

Interpret the Graph Below: Just like the previous graph, this graph shows an object moving with constant velocity (speed with direction). The object is returning to a starting point

Interpret the Graph Below: The curve in the graph shows that the object’s velocity is changing as time passes.

Interpret the Graph Below: In the first part of the graph the object is moving with constant velocity. In the second part of the graph the object is at rest (not moving, no change in distance). In the third part the object is again moving with constant velocity.

Review – Velocity l What is the average speed of an object that travels 100 meters in 20 seconds? A. B. C. D. l 4 m/s 8 m/s 5 m/s 10 m/s Which of the following is NOT needed to determine the velocity of a moving truck? A. the mass of the truck B. the distance it travels C. the time it takes to travel that distant D. the direction in which it is traveling

Acceleration l l rate at which an object’s velocity changes shows change per unit of time acceleration = final velocity - starting velocity time Recorded in units per units squared l l such as m/s 2 (meters per second squared) to graph l l label time on the x-axis label velocity on the y-axis

Acceleration l l Acceleration is not just “speeding up. ” It is the rate at which velocity changes. Acceleration is: l l l Changing its speed. Changing its direction. Or both! An increase in velocity is commonly called positive acceleration. A decrease in velocity is commonly called negative acceleration or deceleration.

Calculating Average Acceleration l

Average Acceleration Practice l What is the average acceleration of a subway train that speeds up from 9. 6 m/s to 12 m/s in 0. 8 s on a straight section of the track heading east?

Interpret the Graph Below: Label the following. Car A – constant speed Car B – accelerating quickly Car C – stopped for gas in the middle of the trip; returned to start

Interpret the Graph Below: The graph shows that the object’s velocity does not change as time passes. It shows constant velocity.

Interpret the Graph Below: The graph shows that the object’s velocity is increasing as time passes – it is accelerating. The straight line shows that it is constant acceleration.

Interpret the Graph Below: The graph shows that the object’s velocity is increasing as time passes – it is accelerating. The curved line shows that it is not a constant acceleration. The faster acceleration was at the beginning.

Interpret the Graph Below: What happened during this event? What story does the graph tell?

Interpret the Graph Below: Label the following. Car A – a swift acceleration Car B – a gradual slowing of acceleration

Interpret the Graph Below: What is each car doing? Car A – Car B – What is each car doing? Car C – Car D – Car E –

Review – Acceleration l An object accelerates if its A. B. C. D. l speed remains constant direction changes mass remains constant motion can be plotted on a graph Which of the following is an example of changing acceleration? A. a train traveling 65 mph south B. a boat sailing west at 5 knots C. a person jogging at 3 m/s 2 along a winding path D. a car stopped at a red light

Ticker Tapes & Speed/Acceleration