Forces Chapter 6 1 What You Already Learned

Forces Chapter 6. 1

What You Already Learned • Velocity is the ratio of the change in position of an object over a period of time. • Acceleration describes a change in velocity of an object.

Acceleration • What may cause an object to experience a change in velocity? – • A is a or . –A may cause an object to speed up. –A may cause an object to slow down. –A may also cause an object to change direction.

Types of Forces • • •

Force • Force is a quantity, therefore it has both and. • The SI unit force is the. – The 1 N = – 1 accelerate a – 1 sized apple. is a derived unit where: is the amount of force required to mass. is about the weight of a medium

Contact vs. Long Range • Some forces act over distances while others act only when two objects are in contact with one another. – exist when two objects are in contact with one another. – Long-range ( ) forces act over distances without a need forces and are long-range forces.

The System and Environment • The object of interest is called the . • The area around the object is called the. FN Fg

Diagram FN FN = Force of Desk on Book System = Fg and the Fg = Force of Gravity on Book diagrams provide a means by which all the acting on a system can be summarized and accounted for, determined.

Newton’s Law • Newton determined that the an object is the object. applied to move it and to the Where F = Force in Newtons m= of the object a= of the object of to of

Newton’s 2 nd Law and Force vs. Acceleration • How does acceleration relate to force? – As the force on an object , the rate of acceleration will. – i. e. Bigger = Bigger m 2 m 1 Acceleration Note: The slope of the line in a F vs. a graph will of the ___ > ___ equal the object. The greater the slope, the greater the

Newton’s 2 nd Law and velocity vs. time (constant force) • Newton’s 2 nd Law indicates that a constant force applied to an object will cause the speed to change at a • i. e. is . Note: Remember from kinematics that the slope of the line is equal to. Time

Newton’s 2 nd Law / Different Mass • If the applied force to a system is held constant and the mass is increased from m 1 to m 2, what would a velocity vs. time graph look like? m 1 Force is Constant m 2 ___ > ___ Time = Acceleration.

Newton’s 2 nd Law / Different Force • If the mass is held constant and the force applied to a system is increased from F 1 to F 2, what would a velocity vs. time graph look like? F 2 Mass is Constant F 1 ___ > ___ Time = Acceleration.

Example: What is the rate of acceleration? • Two people are pushing a stalled car. The mass of the car is 1850 kg. One person applies a 275 N force while the other applies a 395 N force. A third force of 560 N acts in in the opposite direction compared to the two people. What is the acceleration of the car?

Diagram the problem Fnet =

State the Known and Unknowns • What is known? – Mass (m) = kg – Force of person #1 (N) = – Force of person#2 (N) = – Opposing Force (N) = • What is not known? – Acceleration (a) = ? N N N

Perform Calculations • Fnet = Where: o Fnet = • Substitute for Fnet and solve for a: o = + oa= oa= o If there was no opposing force, how would the rate. of acceleration change? o What do you think is the source of the opposing. force?

Key Ideas • Force is a quantity that is a measure of the magnitude of a push or pull in Newtons. • Forces exist as or. • Use to represent forces when problem solving. • Newton’s 2 nd Law of Motion states that the rate of acceleration of an object is to the applied and to its mass. – A constant force applied to an object will cause it to accelerate at a. – As force , increases. – As mass , decreases.