Transcript Chapter 4
Chapter 4 9/20/2012 nd 2 Newton’s Law ~ Newton’s 2nd law of motion says that a net force acting on an object causes the object to accelerate in the direction of the force. ~The acceleration is determined by the size of the force and the mass of the object. ~A larger mass requires a greater force than a smaller mass would require to achieve the same acceleration. The Force Equation! nd • Newton’s 2 Law can be expressed in a equation form like this: Force = mass x acceleration F= ma Mass is expressed in kilograms and acceleration is expressed in m/s2. A newton is the amount of force needed to accelerate an object with a mass of 1kg at an 2 acceleration of 1m/s . In other words, 1 N = 1 kg x m/s2. Acceleration Caused by Gravity! At the Earth’s surface, gravity causes all falling objects to accelerate at 9.8 m/s2. Because any force can be calculated by using this equation: F =m x a. The weight of an object(W) is the force of gravity acting on its mass. W = m x a. So the last equation we could do would be W = m x 9.8m/s2 Acceleration due to gravity is the same for all objects, regardless of the mass. Air resistance is the force air exerts on a moving object. This force acts in the opposite direction to that of the objects motion. In case of a falling object, air resistance pushes up as gravity pulls down. Terminal Velocity is the highest velocity that will be reached by a falling object. Air Resistance gradually increases until it balances the pull of gravity. Projectiles and Circular Motion Projectiles! A projectile is anything that’s been thrown or shot through the air. ~Horizontal Motion~ Horizontal motion that is, motion parallel to the Earth’s surface. Vertical Motion! • Vertical motion is when gravity starts pulling it downward, or motion perpendicular to Earth’s surface. Gravity exerts an unbalanced force to the ball. Gravity exerts an unbalanced force to the ball,changing the direction of it’s path from forward only to forward and downward. Motion Along Curves • Centripetal Acceleration is when acceleration toward the center of a curved or circular path. The word centripetal means” toward the center” ~Centripetal Force~ • This is when the force is acting toward the center of a curved or circular path. • When a car rounds a sharp curve on a highway, the centripetal force is the friction between the tires and the road surface. *Weightless in Orbit* • To be truly weightless, the astronauts would have to be free from the effects of gravity. • Orbiting 400 km above Earth, the shuttle and everything inside it still respond to those effects. • In fact, the gravity keeps the shuttle in orbit just like when the astronauts do when they leave the shuttle in space. • The object would seem to be weightless. • When an object is influenced only by gravity, it is said to be in free-fall. • An orbiting space shuttle and all it’s contents are in free-fall around Earth. When you are up there in space you would see like in movies that when you are floating in the air so are the other objects around you.