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## Forces and Motion Study Guide

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**Speed is the rate of change over time.**• What is momentum? What is The Law of Conservation of Momentum? Momentum = mass x velocity. LOCOM = the momentum of a system is constant if there are no outside forces acting on the system. • What is inertia? Give an example. An objects resistance to motion. A rock has more inertia than a pebble. • What is a force? A push or a pull**What are balanced and unbalanced forces? Give an example.**Balanced forces have a net force of zero, unbalanced do not have a zero net force when added or subtracted. Balanced = an object at rest, Unbalanced = an object in motion • When a toy truck collides with a toy car what happens to the momentum of the car and the truck before and after the collision? Momentum of the system stays the same before and after the collision because of The Law of Conservation of Momentum. • What type of force does Earth exert on a ball thrown into the air? Gravitational Force *When the only force acting on an object is gravity the object is in free fall. • How is velocity different than speed? Velocity is a measure of motion plus direction and speed is just a measure of motion, no direction is given.**What is acceleration? a measure of change in velocity**• Describe three different ways a change in acceleration can occur? increase acceleration, decrease acceleration, change direction • What causes a leaf and an acorn to fall at different rates? Air resistance. There is a greater amount of air resistance acting on the leaf because the leaf has more surface area than the acorn • Explain the action and reaction forces that occur as you walk? Action Force = you push your foot down on the Earth when you’re moving forward. Reaction Force = the Earth pushes back up on your foot.**When graphing an object in motion what goes on the**horizontal axis? Vertical axis? horizontal axis = time, vertical axis = distance, speed, or velocity depending on what your graphing • What is the average speed of an object that travels 100 meters in 5 seconds? 20 m/s • What is the upward force on an object falling through the air? Air Resistance • What are vector arrows? What do they tell you about objects in motion? Arrow that show forces acting on an object in a diagram. Strength and direction**Draw a sketch of a book sitting on a table. Draw vector**arrows to show forces acting on the book. Label the forces acting on the book. • Whenever an object is in motion what is opposing the motion? Friction • What is gravitational force? What two things affect the strength of gravitational force between two objects? GF = attraction between all objects, mass and distance of two objects affect gravitational force • Define motion? a change in position of an object over time**What is static friction? Give an example. Friction that**occurs between two or more solid object that are NOT moving relative to each other. Ex: pencil sitting on a desk • What is rolling friction? Give an example. Friction that occurs when a round surface rolls over another surface. Ex: a ball rolling down a street or pushing a grocery buggy. • What is sliding friction? Give an example. Friction created between two objects sliding or rubbing against each other. Ex: rubbing your hands together or a box sliding across the floor. • What 3 things are needed to determine the velocity of a moving truck? distance moved, time it took to move given distance, and direction**What is the term for a rate of change in velocity?**Acceleration • What is the measure of inertia? mass • Speed measures change in what? distance over time • What is the amount of matter in an object called? mass • What is average speed? Total distance traveled over total time. *On a long trip you might slow down and speed up along the way. When someone asks how fast you drove you probably give them your average speed. • What is instantaneous speed? On the long trip instantaneous speed is the speed you were going at one specific moment in time.**Suppose that Boy A exerts a force of 3000 Newtons on the box**and Boy B exerts a force of 5000 Newtons in the opposite direction. • Draw arrows showing the individual and combined forces of the box in the picture below. • What is the combined force (net force) on the box? __2000 Newtons_______________ • Are the forces balanced or unbalanced? __unbalanced, so the box is probably moving_ 32. Could there ever be a case when Boy A and Boy B are both exerting a force on the box but the box doesn't move? Yes, if the forces are equal and in opposite directions. 3000 N 5000 N 2000 N A B**Describe the object’s motion the first 4 seconds? Moving**forward at a constant rate Describe the object’s motion at 5 seconds? Not moving Describe the object’s motion the last 3 seconds? Going backwards**Graph A**• Describe the object’s motion in each of the following graphs. Moving a constant speed, speed stays the same. Speed is increasing at a constant rate. Speed is decreasing at a constant rate. Graph B Graph C**What is Newton’s 1st Law of Motion? Give an example. An**object at rest will remain at rest unless acted on by an outside force, also known as law of inertia, deals with balanced forces. Ex: table cloth trick • What is Newton’s 2nd Law of Motion? Give an example. The acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object, F=MA Ex: Increasing the mass of a car will increase its momentum when in motion • What is Newton’s 3rd Law of Motion? Give an example. For every action there is an equal and opposite reaction, deals with action and reaction forces. Ex: For a bird to fly upwards, it must flap it’s wings in a downward motion (action force). The air under the bird is compressed and pushes back up on the bird (reaction force). • What is Centripetal Force? Give an example. Any motion in a curved path represents accelerated motion, and requires a force directed toward the center of curvature of the path. Ex: Ice skater spinning