2D Motion

Freefall Post Lab AB NA BC CD Analyzing Data Interval Interval Dist. (cm) Increase dist.(cm) Interval Time (s) Average Vel. (m/s) Accel. (m/s2) AB NA BC BC-AB CD CD-BC

Freefall Post Lab First Graph Questions What’s the shape of the graph? What does the shape of graph infer about the motion of the tape? What does the y-intercept represent? What does the slope of a line tangent to the curve represent? Is the tape moving at point A? Explain. Which of our basic equations best fits the graph? What does this acceleration represent?

Freefall Post Lab Second Graph Questions What’s the shape of the graph? What does the shape of graph infer about the motion of the tape? What does the y-intercept represent? What does the slope of the curve represent? Is the tape moving at point A? Explain. Which of our basic equations best fits the graph? Calculate the acceleration of the tape. What does this acceleration represent?

Freefall Post Lab Define Freefall Any condition in which the only force affecting your motion is gravity.

Example #1 A brick is dropped from the roof of a building under construction. The brick strikes the ground after 4.85 seconds. What’s the brick’s velocity just before it reaches the ground?

Example #1 A brick is dropped from the roof of a building under construction. The brick strikes the ground after 4.85 seconds. How tall is building?

Example #2 A kangaroo is playing catch with herself by kicking a ball straight up. How fast does she kick the ball if the ball comes back to her foot 2.5 seconds later?

Example #2 A kangaroo is playing catch with herself by kicking a ball straight up. How high did the ball rise?

Freefall Ball-Terminal Velocity Post Lab Part 1 Describe the acceleration of ball as it rises, reaches the top, and falls. Ignore Air Resistance. FBD’s Ball as it leaves hand Ball at top of flight Ball Falling

Freefall Ball-Terminal Velocity Post Lab Terminal Velocity-Definition Factors affecting the force of air resistance

Position vs. time graph for freefalling coffee filters Freefall Ball-Terminal Velocity Post Lab Part 2 (a)How does the terminal velocity seem to depend on the mass of the coffee filters (number of coffee filters)? (b) What is the acceleration of the coffee filters when they reach terminal velocity? (c) How can you tell what the terminal velocity of the coffee filters is from the position versus time graph? Position vs. time graph for freefalling coffee filters

Freefall Ball-Terminal Velocity Post Lab Part 2 (d) If we could remove all of the air from the room, describe the free fall acceleration of a softball inflated balloon coffee filter feather bowling ball Parachute Explain your answers.

Example #3 A 0.005 kg coffee filter is dropped from rest from a height h above the floor. The filter falls for 1 s before reaching terminal velocity. What is the filter’s acceleration immediately (at t = 0 s),and after it is dropped?

Example #3 A 0.005 kg coffee filter is dropped from rest from a height h above the floor. The filter falls for 1 s before reaching terminal velocity. What is the filter’s acceleration when it reaches terminal velocity?

Example #3 A 0.005 kg coffee filter is dropped from rest from a height h above the floor. The filter falls for 1 s before reaching terminal velocity. What is the magnitude of the air resistance force while falling at terminal velocity? FBD at terminal velocity

Projectile Motion Post Lab Questions Define projectile: Any object moving through space above the surface of the earth acted on only by earth’s gravity Define trajectory: The path of a projectile. It is always curved.

Projectile Motion Post Lab Questions 3. Do the horizontal and vertical motions affect one another? Explain your answer using the data from your lab. The horizontal and vertical motion of the projectile are independent of one another! The HORIZONTAL VELOCITY is CONSTANT (ignore air resistance) The VERTICAL ACCELERATION is always 9.8 m/s2 downward

Projectile Motion Post Lab Questions 4. Write an equation that describes horizontal motion in terms of horizontal speed (vx), horizontal distance (dx) and time of travel (t). dx = vxt

Projectile Motion Post Lab Questions 5. Write an equation that describes the vertical motion in terms of distance fallen (dy), vertical accel. (g) and time of travel (t). dy = ½gt2

Projectile Motion Velocity can be SEPARATED into horizontal and vertical components. Solve vertical and horizontal parts of problem separately. ALL the same equations from linear motion work for projectiles. Time is the only quantity which is the same for both vertical and horizontal motion. See the Kin/Dyn Skill Sheet Horizontal Vertical

Example #4 A stone is thrown horizontally at 25 m/s from the top of a cliff 53 meters high. How long does it take the stone to reach the bottom of the cliff?

Example #4 A stone is thrown horizontally at 25 m/s from the top of a cliff 53 meters high. How far from the base of the cliff does the stone strike the ground?

Example #4 A stone is thrown horizontally at 25 m/s from the top of a cliff 53 meters high. What’s the stone’s horizontal and vertical speeds just before striking the ground? vfy vfx

Example #5 Cliff divers at Hawaii dive from 65 meter high cliffs. The rocks at the base of the cliff protrude 27 meters beyond the edge of the cliff. What is the minimum horizontal velocity needed to safely clear the protruding rocks?