An object?s mass is a measure of its inertia. The more mass, the more force is required to obtain a given acceleration. A constant force is acting on an object. Which of these graphs best represents the velocity of the object? A single force is acting on an object. Which type of motion is not physically allowed? A. the object speeds up B. the object is at rest C. the object slows down D. the object's motion changes direction §4.4 Interaction Pairs: Newton?s Third Law of Motion Newton?s 3rd Law: When 2 bodies interact, the forces on the bodies from each other are always equal in magnitude and opposite in direction. Or, forces come in pairs. A ping-pong ball collides with a bowling ball. Which experiences the greatest force? A. The ping-pong ball B. The bowling ball C. They experience the same force D. The force on each depends on its velocity. E. The force on each depends on its mass. A book is sitting on a desk top. Identify the 3rd law partner of the weight of the book. A. The force of the desk on the book. B. The force of the book on the desk. C. The force of the earth on the book. D. The force of the book on the earth. External forces: Any force on a system from a body outside of the system. Internal forces: Force between bodies of a system. § 4.5 Gravitational Forces Gravity is the force between two masses. Gravity is a long-range or field force. No contact is needed between the bodies. The force of gravity is always attractive! Here F = the force the Earth exerts on mass M2. This is the force known as weight, w. the gravitational force per unit mass. This is called the gravitational field strength. It is also referred to as the acceleration due to gravity.
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