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Motion and Force • Chapter Twelve: Distance, Time, and Speed • Chapter Thirteen: Forces • Chapter Fourteen: Force and Motion Chapter Fourteen: Force and Motion • 14.1 Newton’s First and Third Laws • 14.2 Newton’s Second Law Investigation 14B Newton’s Second Law • What is the relationship between force and motion? 14.2 Newton’s Second Law • Acceleration is the rate at which your velocity (speed with direction) changes. 14.2 Acceleration • • A car can change its velocity by speeding up, slowing down, or turning. If an object’s acceleration is zero, the object could be moving at a constant speed in a straight line or could be stopped. • To calculate acceleration, you divide the change in speed by the amount of time it takes for the change to happen. 14.2 Acceleration • • If an object speeds up, it has a positive acceleration. If it slows down, it has a negative acceleration. What is the acceleration of the sailboat? 14.2 Force, mass and acceleration • Force causes acceleration, and mass resists acceleration. • Newton’s second law relates the force on an object, the mass of the object, and its acceleration. • Force causes acceleration, and mass resists acceleration. • The stronger the force on an object, the greater its acceleration. – Force is directly proportional to acceleration. – If twice the force is applied, the acceleration is twice as great. • The greater the mass, the smaller the acceleration for a given force. – Mass is inversely related to force. – An object with twice the mass will have half the acceleration if the same force is applied. 14.2 Applying the second law • Keep the following important ideas in mind: 1. The net force is what causes acceleration. 2. If there is no acceleration, the net force must be zero. 3. If there is acceleration, there must also be a net force. 4. The force unit of newtons is based on kilograms, meters, and seconds 14.2 Newton’s second law and gravity • Gravitational force exists between all objects that have mass. • An object is in free fall if it is accelerating due to the force of gravity and no other forces are acting on it. • Objects in free fall on Earth accelerate downward at 9.8 m/s2, the acceleration due to gravity. 14.2 Newton’s second law and gravity • An object is in free fall if it is accelerating due to the force of gravity and no other forces are acting on it. • Objects in free fall on Earth accelerate downward at 9.8 m/s2, the acceleration due to gravity. 14.2 Universal gravitation • Gravitational force exists between all objects that have mass. • You do not notice gravity between ordinary objects because it takes a huge amount of mass to create enough force to notice. 14.2 Universal gravitation • The force of gravity between you and Earth is strong because the planet’s mass is huge. • Newton’s law of universal gravitation says the strength of the force depends on the mass of the objects and the distance between them. 14.2 Orbital motion • Newton’s second law can be used to explain the motion of planets, moons, and satellites in orbit. • The orbiting moon falls around Earth. Can kick a soccer ball into orbit? Can you we launch a soccer ball into orbit? Activity Making a Spool Car • Newton’s three laws can be used to explain the motion of everyday objects. • In this activity you will build a car and apply Newton’s laws to explain how it works and why it moves as it does.