Transcript lecture4.2
CHAPTER 4 Forces and Newton's Laws of Motion 4.5 Newton's Third Law of Motion 4.5 Newton's Third Law of Motion 4.5 Newton's Third Law of Motion Whenever one body exerts a force on a second body, the second body exerts an oppositely directed force of equal magnitude on the first body. Examples of Newton's 3rd Law Example 4 Suppose that the mass of the spacecraft in Figure 4.7 is mS = 11 000 kg and that the mass of the astronaut is mA = 92 kg. In addition, assume that the astronaut exerts a force of P = +36 N on the spacecraft. Find the accelerations of the spacecraft and the astronaut. Example 4 Suppose that the mass of the spacecraft in Figure 4.7 is mS = 11 000 kg and that the mass of the astronaut is mA = 92 kg. In addition, assume that the astronaut exerts a force of P = +36 N on the spacecraft. Find the accelerations of the spacecraft and the astronaut. Astronauts use a tether to stay connected to the space capsule. Application of Newton's Third Law Some rental trailers include an automatic brake-actuating mechanism. 4.6 Types of Forces: In nature there are two general types of forces, fundamental and non-fundamental. Fundamental forces: •Gravitational force •Strong nuclear force •Weak nuclear force-----| •Electromagnetic force--!—Electroweak force Non-fundamental forces: Pushing, Pulling, Kicking, Grabbing, etc…. These are related to the electromagnetic force. They arise from the interactions between the electrically charged particles that comprise atoms and molecules. Fundamental Forces Fundamental Force Strong nuclear Example Nucleus Electromagnetic +, - Charges Particles Affected Nuclear Relative Strength 1 Charged 10-2 Weak nuclear Radioactivity Nuclear 10-15 Gravitational Your weight 10-38 All Unification of Fundamental Forces Newton’s Law of Universal Gravitation Every body in the universe attracts every other body with a force that is directly proportional to the product of the masses of the bodies and inversely proportional to the square of the distance between the bodies. Newton’s Law of Universal Gravitation Every body in the universe attracts every other body with a force that is directly proportional to the product of the masses of the bodies and inversely proportional to the square of the distance between the bodies. Universal Gravitational Constant m1m2 11 F G 2 ; G 6.67 10 (SI ). r Universal Gravitational Constant m1m2 11 F G 2 ; G 6.67 10 (SI ). r The proportionality constant, G is called the universal gravitational constant. Its value in the SI system of units is, G = 6.67 10-11N.m2/Kg2. Universal Gravitational Constant m1m2 11 F G 2 ; G 6.67 10 (SI ). r The proportionality constant, G is called the universal gravitational constant. Its value in the SI system of units is, G = 6.67 10-11N.m2/Kg2. The law of gravitation is universal and very fundamental. It can be used to understand the motions of planets and moons, determine the surface gravity of planets, and the orbital motion of artificial satellites around the Earth. Acceleration Due to Gravity Acceleration Due to Gravity Acceleration Due to Gravity Acceleration Due to Gravity Calculate g for planet Earth at sea level. Weight Weight = Mass x Gravity W m g The weight of an object is the gravitational force that the planet exerts on the object. The weight always acts downward, toward the center of the planet. SI Unit of Weight: : newton (N) The Hubble Space Telescope Example 6 The mass of the Hubble Space Telescope is 11 600 kg. Determine the weight of the telescope (a) when it was resting on the earth and (b) as it is in its orbit 598 km above the earth's surface. 4.8 The Normal Force The normal force FN is one component of the force that a surface exerts on an object with which it is in contact, namely, the component that is perpendicular to the surface. Normal Force Is Not Always Equal to the Weight Elevator Ride What happens to your weight during an elevator ride? Apparent Weight Apparent Weight