1. SACE Stage 1 Conceptual Physics Newton’s Second Law of Motion – Force and Acceleration

2. Force Causes Acceleration Forces are what produce accelerations. Forces are what produce accelerations. Acceleration is caused by forces. Force is proportional to acceleration. Acceleration is caused by forces. Force is proportional to acceleration. F  a

3. Force Causes Acceleration When objects accelerate, it can be caused by a number of different forces. This supplies a net force on the object. When objects accelerate, it can be caused by a number of different forces. This supplies a net force on the object. Applet – Net Force Applet – Net Force

4. Mass Resists Acceleration Acceleration depends on the mass being pushed Acceleration depends on the mass being pushed Greater the mass, the less the acceleration. Greater the mass, the less the acceleration. Greater the acceleration, smaller the mass. Greater the acceleration, smaller the mass.

5. Mass Resists Acceleration For a given force, the acceleration produced is inversely proportional to the mass. For a given force, the acceleration produced is inversely proportional to the mass.

6. Mass Resists Acceleration

7. Newton’s Second Law Definition – The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force and is inversely proportional to the mass of the body. Definition – The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force and is inversely proportional to the mass of the body.

8. Newtons Second Law Experiment Using the applet, determine the acceleration of the block. Using the applet, determine the acceleration of the block.

9. Statics How many forces are acting on these stationary objects! How many forces are acting on these stationary objects!

10. Friction Friction is caused largely due to the irregularities in the 2 surfaces of the objects. Friction is caused largely due to the irregularities in the 2 surfaces of the objects. If viewed under a microscope, the even the surface of a mirror will appear rough. If viewed under a microscope, the even the surface of a mirror will appear rough.

11. Friction Friction always acts in the opposite direction of the motion. Friction always acts in the opposite direction of the motion.

12. Friction - Questions Suppose a high flying jet cruises at constant velocity when the thrust of its engines is a constant 80 000N. What is the acceleration of the jet? What is the force of air resistance acting on the jet? Suppose a high flying jet cruises at constant velocity when the thrust of its engines is a constant 80 000N. What is the acceleration of the jet? What is the force of air resistance acting on the jet?

13. Friction - Questions Answer – The acceleration is zero because the velocity is constant. As the acceleration is zero, the net force must be zero, therefore the thrust must equal the amount of air resistance on the jet, i.e., 80 000N in the opposite direction of the velocity.

14. Applying Force - Pressure You can place a book on the table and no matter what way you place it, the force will always be the same. You can check this by using a bathroom scale. The book on the right is exerting more pressure on the table than the book on the left.