Forces and Motion: Force and Acceleration PDF

LESSON 2 Forces and Motion Force and Acceleration Key Concept What happens to the motion of a water tube What do you think? Read the two statements below and decide when it’s pushed or...

LESSON 2 Forces and Motion Force and Acceleration Key Concept What happens to the motion of a water tube What do you think? Read the two statements below and decide when it’s pushed or whether you agree or disagree with them. Place an A in the Before pulled? column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind. Before Statement After You can calculate average acceleration by dividing the change in velocity by the change in distance. An object accelerates when either its speed or its direction changes. Mark the Text Identify the Main Ideas Highlight the main idea in What can cause a change of motion? Recall that velocity changes if either speed or direction each paragraph. Underline the details that support the changes. When a car moves faster, its velocity increases. When a main idea. car slows down, its velocity decreases. If the car turns, its velocity changes because its direction changes. Changes in Motion When the car’s velocity changes, the car is accelerating. Acceleration Is a measure of the change in velocity during a period of time. An object accelerates when its velocity Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. changes as a result of increasing speed, decreasing speed, or a change in direction. Like velocity, acceleration has a direction. Acceleration can be represented by an arrow. The length of the arrow shows the amount of acceleration. The direction of an acceleration arrow depends on whether velocity is increasing or decreasing. 8 Forces and Motion Reading Essentials THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Forces Think about all the things you pushed or pulled today. You might have pushed toothpaste out of a tube. Maybe you pulled out a chair to sit down. A push or a pull on an object is called a force. An object or a person can apply a force to another object or person. Some forces are applied only when objects touch. Other forces are applied even when objects do not touch. You have probably seen a musician strike the keys of a piano or an athlete hit a ball with a bat. The person or object applies a force to an object that it touches. A contact force is a push or a pull on one object by another that is touching it. Contact forces can be weak. When you press the keys on a Academic Vocabulary computer keyboard, the contact force is weak. They can also be weak strong. The plates, or rock slabs, that make up Earth’s crust can (adjective) having little apply strong contact forces against each other. Over long power or force periods of time, these forces can be strong enough to form mountain ranges if one plate pushes another plate upward. Scientific Vocabulary crust Mathematical Model Newton’s second law of motion (noun) a hard covering on describes the relationship between an object’s acceleration and something's surface the net force that acts on the object. According to Newton’s second law of motion, the acceleration of an object is equal to Scientific Vocabulary the net force acting on the object divided by the object’s mass. range The direction of acceleration is the same as the direction of the (noun) a group of net force. mountains or hills in a line Newton’s Second Law Equation net force (in N) acceleration (in m/s2) = mass (in kg) F a= m SI units are included in the equation. Acceleration is expressed in meters per second squared (m/s2 ), mass in kilograms (kg), Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. and force in newtons (N). A newton is the same as kg m/s2. How does friction affect motion? Why does a baseball player slow down as he slides into a base? Friction is a contact force that resists the sliding motion between two objects that are touching. Friction The force of friction acts in the opposite direction of the motion. Friction is a force that resists the sliding motion of two surfaces that are touching. As he slides to the base, the player must overcome friction from the ground, which is exerting a force away from the base. Rougher surfaces produce greater friction than smooth surfaces. Other factors, such as the surface area and the weight of an object, also affect the force of friction. Reading Essentials Forces and Motion 9 THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Friction and Newton’s Laws Imagine a book sitting on a table. When you push the book, the book moves. This is because the force you apply to the book is greater than the friction between the book and the table. The book moves in the direction of the greater force. If you stop pushing, friction stops the book, just like the friction between tires and the road stops a car. What would happen if there were no friction between the book and the table? According to Newton’s second law, the book would continue to move at the same speed in the same direction unless a force changed its motion. The book stopping is evidence that friction is acting on the book. How do multiple forces change motion? Force has both size and direction. Arrows can be used to show the size and direction of a force. Usually more than one force is acting on an object at a time. The forces can be added together to find the net force. The net force is the sum of all the Scientific Vocabulary forces acting on an object. The net force can be modeled with a diagram free-body diagram. A free-body diagram is a simple model that (noun) a drawing that can help you understand the forces acting on an object. shows the parts of something How can forces act on an object that is not changing its motion? Newton’s First Law Sir Isaac Newton studied how forces affect the motion of objects. He developed three rules that are known as Newton’s laws of motion. Newton’s first law of Academic Vocabulary motion states that if the net force on an object is zero, the results motion of the object does not change. As a result, balanced (noun) information or forces and unbalanced forces have different results when they Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. answers produced by act on an object. examining something carefully and scientifically Balanced and Unbalanced Forces According to Newton’s first law of motion, balanced forces cause no change in the motion of an object. This is true when an object is at rest or in motion. A dresser is at rest before anyone pushes on it. It Scientific Vocabulary remains at rest when balanced forces are applied. Both gravity air resistance and air resistance act on the motion of a parachutist. Gravity (noun) how air slows pulls the parachutist toward the ground. Air resistance against down a moving object the parachute slows the fall. When the air resistance and gravity on the parachutist are balanced, the parachutist moves downward with a constant velocity known as terminal velocity. Recall that velocity is the speed and the direction of motion. Terminal velocity is the constant velocity reached when air resistance equals the force of gravity on a falling object. 10 Forces and Motion Reading Essentials THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.  Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind? Copyright © McGraw-Hill Education. Permission is granted to reproduce for classroom use. Reading Essentials Forces and Motion 11 THIS MATERIAL IS PROVIDED FOR INDIVIDUAL EDUCATIONAL PURPOSES ONLY AND MAY NOT BE DOWNLOADED OR FURTHER DISTRIBUTED.