2 Unbalanced Forces & Velocity Whenever an object’s speed or direction changes, an unbalanced force must be acting on the object.
3 Unbalanced Forces & Velocity When a resting object is acted on by an unbalanced force, the object will accelerate in the direction of the unbalanced force.
4 Unbalanced Forces & Velocity An object’s speed will increase when a net force acts in the same direction as the object’s motion.
5 Unbalanced Forces & Velocity An object’s speed will decrease when a net force acts in the opposite direction of the object’s motion.
6 Unbalanced Forces & Velocity Unbalanced forces can cause an object to speed up, slow down, or change direction.The rail exerts an unbalanced force on the ball, changing the ball’s motion.
7 Unbalanced Forces & Velocity A ball tied to a string and swung in a circle is an example of circular motion.
8 Unbalanced Forces & Velocity During circular motion, the centripetal force acts perpendicular to the velocity, toward the center of the circle.
9 Newton’s Second Law of Motion When an object changes speed or direction, its velocity changes, and the object is accelerating.
10 Newton’s Second Law of Motion Newton’s Second Law of Motion states that the acceleration of an object equals the net force divided by the object’s mass.a = F ÷ mF = ma
11 Newton’s Second Law of Motion In the equation representing Newton’s Second Law of Motion:Force is measured in Newtons (N)Mass is measured in kilograms (kg)Acceleration is measured in meters/second2 (m/s2)
12 Newton’s Second Law of Motion F = ma↑ force = ↑ acceleration↑ mass = ↓ acceleration
13 Newton’s Second Law of Motion When the net force is zero, the acceleration is zero.When the acceleration of an object is zero, the velocity is constant.
14 Newton’s Second Law of Motion When the fluid friction force (air resistance) is equal to the gravity force (weight), an object reaches its terminal velocity.It no longer accelerates, and will remain at whatever velocity it was already traveling.
15 Newton’s Second Law of Motion Terminal velocity for a human is mph.
16 Newton’s Second Law of Motion When the net force is NOT zero, the velocity of the object changes.
17 Newton’s Third Law of Motion Newton’s Third Law of Motion states that when one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first object.
18 Newton’s Third Law of Motion The forces two objects exert on each other are called force pairs.The forces in a force pair are equal in size, and opposite in direction.
19 Newton’s Third Law of Motion One of the forces in a force pair is called the action force and the other force is called the reaction force.
21 B opposite to the object’s motion C toward the center of the circle 2.3 Unbalanced Forces and AccelerationIn what direction does the net force of an object moving with constant speed and in a circular motion occur?A downwardB opposite to the object’s motionC toward the center of the circleD in the direction of the object’s velocity
22 Acceleration depends on both the force applied and ____. 2.3 Unbalanced Forces and AccelerationAcceleration depends on both the force applied and ____.A distance from the objectB speed of the objectC mass of the objectD normal force of the object
23 A The motion does not change. B The object speeds up. 2.3 Unbalanced Forces and AccelerationHow does the motion of an object traveling in a straight line at 5 m/s change if a balanced force is applied?A The motion does not change.B The object speeds up.C The object slows down.D The object travels in a horizontal circle.
24 What would cause an object to have a larger acceleration? A increasing the net force appliedB decreasing the net force appliedC increasing the mass and keeping the net force constantD none of the above
25 What causes a change in motion on an object? A zero net forceB unbalanced forceC weightD balanced force
26 For every action force, there is a reaction force that is ____. A in the same directionB equal to the two objectsC equal and in the opposite directionD unequal and in the direction of the object with less mass
27 You throw a 2 kg ball with a force of 50 N You throw a 2 kg ball with a force of 50 N. What is the ball’s acceleration?A 25 m/s2B 48 m/s2C 52 m/s2D 100 m/s2
28 SCI 2.fA tennis ball hit by a racket has an acceleration of 1000 m/s2. If the net force on the tennis ball is 100 N, what is the tennis ball’s mass?A 0.01 kgB 0.1 kgC 1 kgD 10 kg