RI Chap 5 Projectile Motion - Lecture Notes

5 PROJECTILE MOTION H2 Physics 9478 Content Page 5.1 Mass vs Weight 2 5.2 Free Fall 2 5.3 One-Dimensional Motion 4 5.4 Two-Dimensional Motion 4 5.5 Work Done & GPE of a Projectile (without air resistance) 10 5.6 Effects of Air Resistance 12 5.7 Appendix 18 Learning Outcomes Candidates should be able to: (a) describe and use the concept of weight as the force experienced by a mass in a gravitational field. (b) describe and explain motion due to a uniform velocity in one direction and a uniform acceleration in a perpendicular direction. (c) derive, from the definition of work done by a force, the equation PE mg h∆=∆ for gravitational potential energy changes in a uniform gravitational field (e.g. near the Earth’s surface). (d) recall and use the equation PE mg h∆=∆ to solve problems. (e) describe qualitatively, with reference to forces and energy, the motion of bodies falling in a uniform gravitational field with air resistance, including the phenomenon of terminal velocity.

Page | 2 5.1 Mass vs Weight i.e. it is a measure of the inertia of a body. The same force, when applied to a body of larger mass will cause a smaller change in motion. Weight or the gravitational force on a body is an extrinsic property as it depends not just on the mass of the body, but also the gravitational field strength g at the point where the body is. Mathematically W mg= It is important not to confuse weight with mass. 5.2 Free Fall  Galileo’s Free Fall Experiment Galileo's free fall experiment is one of his most famous contributions to physics. It involved the study of bodies falling freely under the influence of gravity. The purpose of the experiment was to challenge the prevailing Aristotelian belief that heavier bodies fall faster than lighter bodies. Galileo hypothesized that in the absence of air resistance, all bodies would fall at the same rate, regardless of their mass. Mass The mass m of a body is the intrinsic property of a body which resists change in motion. Weight The weight W of a body is the force experienced by a mass in a gravitational field.

RAFFLES INSTITUTION YEAR 56 PHYSICS DEPARTMENT Page | 3  Acceleration Since the gravitational force is the only force acting on a falling body, netF mg= By Newton’s 2nd Law, mg ma ag = = Thus, the acceleration of the body is dependent on the gravitational field strength, i.e. ag= . The acceleration of a free-falling object near the surface of the Earth has an average value of 29.81 m s− . This is known as the acceleration of free fall. Professor Brian Cox visits NASA’s Space Power Facility in Ohio to see what happens when a bowling ball and a feather are dropped together in the world’s biggest vacuum.  Free Falling Bodies in a Uniform Gravitational Field An object moving freely near the surface of the Earth in the absence of air resistance is said to be undergoing free fall. In