The area under an acceleration-time graph gives the change in velocity
Motion & Kinematics - OCR A-Level Physics
- The area under an accelerationThe rate of change of velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.. A vector quantity. Measured in m s⁻².-time graph gives the change in velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.
- A horizontal line indicates constant accelerationThe rate of change of velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.. A vector quantity. Measured in m s⁻².
- A line at $a = 0$ indicates constant velocity (no accelerationThe rate of change of velocity. A vector quantity. Measured in m s⁻².)
- An a-t graph for free fallMotion under gravity alone, with no other forces acting. All objects in free fall near Earth's surface have the same acceleration, g = 9.81 m s⁻². is a horizontal line at a = 9.81 $m s^{-2}$ (or -9.81 depending on sign convention)
- An a-t graph for an object reaching terminal velocityThe constant velocity reached when the driving force on an object is exactly balanced by resistive forces, so the resultant force is zero. shows acceleration decreasing from g to zero
Examiner Tips and Tricks
- Students are often asked to sketch a-t graphs for falling objects.
- For free fallMotion under gravity alone, with no other forces acting. All objects in free fall near Earth's surface have the same acceleration, g = 9.81 m s⁻².: horizontal line at g.
- For falling with air resistanceThe opposition to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). flow. The ratio of potential difference to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A).. Measured in ohms (Ω).: starts at g, curves down to zero as the object reaches terminal velocityThe constant velocity reached when the driving force on an object is exactly balanced by resistive forces, so the resultant force is zero..