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English for students of Physics_Unit 9

Perhaps nothing is so ingrained in our senses as the perpetual pulling of the earth on our surroundings. It’s always there, never changing. It’s been hugging solids, liquids and gases to the earth’s surface for over 4 billion years. Earth’s gravity is built into our descriptions of our world with words like up, down, and weight. Exactly what is weight? A weight is a force, nothing more. Your weight is the pull of earth’s gravity on your body. Likewise, the weight of your car is the force of the earth’s attraction for it. The greater the mass is, the. | 49 Unit Nine WEIGHT AND MASS READING PASSAGE Weight and weightlessness Perhaps nothing is so ingrained in our senses as the perpetual pulling of the earth on our surroundings. It s always there never changing. It s been hugging solids liquids and gases to the earth s surface for over 4 billion years. Earth s gravity is built into our descriptions of our world with words like up down and weight. Exactly what is weight A weight is a force nothing more. Your weight is the pull of earth s gravity on your body. Likewise the weight of your car is the force of the earth s attraction for it. The greater the mass is the larger the attraction. Two identical pickup trucks weigh exactly twice as much as one. But mass and weight are not the same they are measures of two different things inertia and force. For example consider the rocks brought from the moon s surface by astronauts. Because of the Earth s stronger gravitational attraction these rocks weigh more on Earth about six times as much as they weighed on the moon. But their mass their resistance to a change in velocity is still the same they have the same quantity of matter on earth as they did on the moon. Even though weight and mass are not the same most of us do not make a distinction between them suppose someone hands you two books and asks which is the more massive. Almost certainly you would weigh one in each hand choose the heavier book. That s okay because the heavier one does have more mass. But if the two books were on a smooth table you could just push each book back and forth to see which has the larger inertia. Their weights don t come into play being balanced by upward pushes from the table . Even then pointing to the one that s harder to accelerate you might from habit still say That one is heavier . The point here is that one is harder to accelerate only because it has greater mass. An astronaut could pick up a large rock on the moon with much less force than required on earth. But if the astronaut shoved