4-3 Newton’s 2nd Law

Recall the definition of acceleration: The cause of acceleration is force.

acceleration ~ net force Force Causes Acceleration Recall that the combination of forces acting on an object is the net force. Acceleration depends on the net force. To increase the acceleration of an object, you must increase the net force acting on it. An object’s acceleration is directly proportional to the net force acting on it: acceleration ~ net force (The symbol ~ stands for “is directly proportional to.”)

Mass Resists Acceleration The acceleration produced depends on the mass that is pushed.

Mass Resists Acceleration The same force applied to twice as much mass results in only half the acceleration. The acceleration is inversely proportional to the mass. (Inversely means that the two values change in opposite directions. As the denominator increases, the whole quantity decreases by the same factor).

Newton’s 2nd Law Equation: ∑F = ma where ∑F is the net force, measured in Newtons (N) m is mass (kg) a is acceleration (m/s2)

Newton’s Second Law Sample Problem A car has a mass of 1000 kg. What is the acceleration produced by a force of 2000 N?

Newton’s Second Law Sample Problem A car has a mass of 1000 kg. What is the acceleration produced by a force of 2000 N?

Working 2nd Law Problems Givens + sketch if needed Draw a free body diagram. Identify numerical data. x-problem and/or y-problem Set up 2nd Law equations in each dimension. SFx = max and/or SFy = may Solve the equations for desired variable. Substitute numbers into equations and simplify.

Sample Problem In a grocery store, you push a 14.5-kg cart with a force of 12.0 N. If the cart starts at rest, how far does it move in 3.00 seconds?

TYPO - this should be m/s2 !

Sample Problem A catcher stops a 92 mph pitch in his glove, bringing it to rest in 0.15 m. If the force exerted by the catcher is 803 N, what is the mass of the ball?