Newton’s Second Law of Motion

Identify three forces acting on a speeding bullet. Bell Work Identify three forces acting on a speeding bullet. Why do cars sometimes skid going around corners on icy roads?

Objectives Define and apply Newton’s second law of motion to real life situations. Relate the acceleration of an object to the mass of the object and the force applied to the object.

Newton’s Second Law of Motion This law states that an unbalanced force on an object causes the object to accelerate in the direction of the force.

Force of wind These forces are unbalanced so the boat accelerates in the direction of the unbalanced force. 20-30 mph Air/Water Resistance

Gravity Unbalanced Forces Table If gravity becomes greater than the upward force of the table, the papers will accelerate downward.

Wagon moves this way Unbalanced Force Applied

Force, Acceleration, and Mass The greater the force applied to a given object, the greater its acceleration.

Force, Acceleration, and Mass For a given force, the greater the mass of an object, the smaller its acceleration and vice-versa.

Newton’s Second Law in Real Life Why would a truck take longer to accelerate when the driver hits the gas if it were loaded with bricks than if it were empty? How might you design a car to achieve maximum acceleration?

Newton’s Second Law in Real Life Using Newton’s second law of motion, explain why larger trucks usually need more distance to stop than do smaller trucks.

Science, Technology, & Sports Friction is the main force that slows the speed of athletes in sports such has skiing, swimming, cycling, speed skating, and running. How can these athletes combat the effects of friction?

Formula for Newton’s Second Law of Motion Newton’s second law of motion can be expressed by the formula F = ma. F stands for force, m stands for mass, and a stands for acceleration.

Formula for Newton’s Second Law of Motion According to this formula, if the force is constant and the mass increases, what will happen to acceleration?

Question Identical twins are riding in identical wagons. A friend gives the first wagon a stronger push than the second. Which twin will experience greater acceleration?

Question Would a car towing a boat take less, the same, or more time to accelerate than it would without the boat? Explain.

Question What will happen to the acceleration of an object if the mass decreases and the force is constant?

Question If two identical objects accelerate at the same rate, what must be true of the force applied to each object?

Review Use Newton’s second law of motion to explain why a free-falling object accelerates. How is the acceleration of an object affected by the force applied to it?

Challenge Using the formula a = f/m, explain why all objects in free fall have the same acceleration, regardless of mass.