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Forces and Force Diagrams. 4.1 pp. 124 - 128 Mr. Richter. Agenda. Warm Up Notes: That’s a Force! Units of Force Types of Forces Force Diagrams Tests Back. Objectives: We Will Be Able To…. Explain how force affects the motion of an object.
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Forces and Force Diagrams 4.1 pp. 124 - 128 Mr. Richter
Agenda • Warm Up • Notes: • That’s a Force! • Units of Force • Types of Forces • Force Diagrams • Tests Back
Objectives: We Will Be Able To… • Explain how force affects the motion of an object. • Distinguish between contact forces and field forces. • Interpret and construct free-body diagrams (FBDs)
Warm-Up: • A car is driving down a flat roadway to the right. What forces do you think are acting on the car (there are at least 4)? What direction do these forces go? • Draw a sketch of a car, and then draw arrows to represent each force you think is present.
Force • Force is a push or a pull acting on an object. • Another way of thinking is that a force changes an object’s velocity. • Force can speed up an object or slow it down. • Force can change an object’s direction. • Force causes acceleration (more on this when we discuss Newton’s Laws of Motion)
Units of Force • The units of force we will most often use in physics are Newtons. • A Newton is the amount of force required to accelerate a 1-kg object 1 m/s2. • [1 N = 1 kg*m/s2] • In the British system, the pound is the unit of force. • 1 pound = 4.448 N
Types of Force • All forces can be broken up into two categories. • Contact force is force that arises from the physical contact between two objects. • catching a baseball, speeding up a car, etc. • Field force is force that exists in the absence of physical contact. • gravity, magnetic force, etc. • Is air resistance a contact force or a field force?
Force Diagrams • Force is a vector quantity, meaning that it has both magnitude and direction. • In complex situations (like a car crashing into a wall), force diagrams help physicists to analyze the situation.
Free-Body Diagrams (FBDs) • To determine the effects of all of the forces acting on one object, a free-body diagram (FBD) is drawn. • Only the forces ACTING ON THE OBJECT are drawn, pointing in the directions in which they act.
FBD Example • Consider the forces acting on the car in the tow truck below.
FBD Practice • Sketch the FBD for the following two situations: • A book lying on a flat table. • A book lying on a ramp with an incline of 15°
Wrap-Up: Did we meet our objectives? • Explain how force affects the motion of an object. • Distinguish between contact forces and field forces. • Interpret and construct free-body diagrams (FBDs)
Homework • p. 128 #2, 3, 5 and 6 • Science Fair • Notebook and Research due Wednesday • Rough draft of Procedure due Wednesday 12/5