Unit 1 Our Dynamic Universe Velocity-Time Graphs CfE Higher Physics Unit 1 Our Dynamic Universe Velocity-Time Graphs

Learning Intentions Can I interpret velocity–time graphs including: a) area under graph is displacement b) gradient is acceleration c) objects in freefall taking into account air resistance and changing surface area. d) change a v-t graph into an a-t graph.

Velocity-time graphs From N5, you will already know the following: The area under these graphs will be the displacement of the object. The acceleration of the object can be found by finding the gradient of the lines.

Velocity-Time Graphs velocity time OA - constant acceleration AB - constant velocity BC - constant deceleration acceleration = gradient of graph displacement travelled = area under graph

Velocity-time graphs As we have previously learned, the direction of the object will tell us if it has a positive or negative value. Remember that UPWARDS is positive and DOWNWARDS is negative. Gravity always acts down. The following graph will show these.

Velocity-Time Graphs – directions B C O F E D - + Positive direction Negative direction OA - constant acceleration CD - constant acceleration AB - constant velocity DE - constant velocity BC - constant deceleration EF - constant deceleration

Velocity-time graphs for objects travelling vertically When a ball is thrown up vertically, we take the following vectors as positive: Displacement Velocity The acceleration due to gravity still acts downwards. What would you expect the graph to look like?

Ball Thrown upwards

Ball Thrown upwards and coming back down At the highest point, you can see that the final speed is 0 m/s https://www.youtube.com/watch?v=3jfoJpIYzXU

Ball thrown up, comes down and hits the ground. Always split the journey into UP and DOWN. As it travels downwards, the final speed now becomes the initial speed. i.e. u = 0 m/s

Some reminders For all of these examples, air resistance is negligible. Acceleration due to gravity is – 9.8 m s-2 At the highest height of travel, the final velocity is ZERO m/s. Velocity and Displacement are positive upwards Velocity and Displacement are negative downwards

The bouncing Ball For an object that is dropped and bounces, what would you expect the velocity- time graph to look like? https://www.youtube.com/watch?v=t511816eZf4

Acceleration-time graphs What would the following velocity – time graph look like as an acceleration – time graph?

v-t Graphs into a-t graphs velocity time A B C O F E D - + acceleration time O - + F A B C D E

Acceleration-Time Graphs + F A B C D E

Success Criteria I can interpret velocity–time graphs including: a) area under graph is displacement b) gradient is acceleration c) objects in freefall taking into account air resistance and changing surface area. d) change a v-t graph into an a-t graph.