Forces Assessment Study Guide

Directions: Use all notes, vocabulary, and practice sheets to complete the study guide. In class, you may also consult your textbook. You may use the internet at home to find additional examples if needed. You will have to apply your knowledge of the material and formulas on the test, as well as interpreting diagrams.

1. Define the following words and give an example of each term.

a. Friction: The force that a surface exerts on another when two surfaces rub together; acts in a direction opposite to the object’s direction of motion. Example: Sliding friction, rolling friction, static friction, fluid friction

b. Balanced forces: Equal forces acting on an object in opposite directions. Example: tug or war when no side is moving, 2 people pushing on in on opposite sides of matchbox car

c. Unbalanced forces: Forces that change an object’s motion. Example: tug of war with uneven numbers or sizes, pushing the matchbox car one direction

d. Mass: The amount of matter in an object. Example: The amount of mass contained by an object would not change on Mars.

e. Centripetal force: A centripetal force causes an object to move in a circle. Example: theme park swing rides which move in a circle

f. Free fall: An object is in free fall when the only force acting on the object is gravity; the object will accelerate until it reaches terminal velocity. Example: dropping a ball of from a cliff g. Weight: The force of gravity on an object at the surface of the planet. Example: Unlike mass, weight will change on the surface of another planet like Mars. h. Gravity: The attractive force between all objects in the universe; strength depends on mass and distance between them. Example: The force that causes a thrown ball to fall to the ground. i. Fluid friction: Friction caused by an object moving through a liquid or gas including air. Example: baseball flying through the air, airplane, rock dropped in bucket of water j. Momentum: Momentum depends on an object’s mass and velocity; momentum will remain the same unless acted upon by an outside force. Example: A semi-truck full of logs has a large mass and must slow down long before a stop light because even with a small velocity, it has a large momentum and is difficult to stop. k. Acceleration: Acceleration depends on the object’s mass and net force acting on the object; increases as force increases if mass stays the same. Example: When you are merging onto a freeway and speed up to fit into the flow of traffic you are accelerating.

2. What are Newton’s Laws of Motion: First Law: An object at rest will remain at rest and an object in motion will remain in motion unless acted upon by an unbalanced force. What is another name for Newton’s First Law?Law of Inertia The amount of inertia an object has depends on its mass. Second Law: Acceleration depends on the object’s mass and on the net force acting on the object. What formulas would you use when applying this law to find: Acceleration: acceleration= net force / mass Unit of measurement:__m/s2____ Force: force=mass x acceleration Unit of measurement:__N____ Mass: mass = net force / acceleration Unit of measurement:___kg___

Third Law: If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. What is an action force?The force exerted by the first object on the second object. What is a reaction force?The force exerted by the second object back on the first. The action and reaction forces in any situation will always be equal and opposite. What formulas would you use when applying this law to find: Momentum: momentum = mass x velocity Unit of measurement: kgm/s Velocity: velocity =momentum / mass Unit of measurement: m/s Mass: mass = momentum / velocity Unit of measurement: kg

3. 1 N is the same as 1 kg m/s2.

4. Calculate the net force for each example. You may not need all of the information provided. a. Net Force 20N

Net Force 10N

c. The Net Force of balanced forces is always O (zero).

Ball A Ball B

4 kg 2 kg

Velocity = 2 m/s Velocity = 0 m/s

a. Calculate the momentum of each ball.

Ball A: 8 kg m/s Ball B: 0 kg m/s

b. If ball A hits ball B, what is the total momentum? 8 kg m/s

Be prepared to explain a similar diagram as this one in terms of action force, reaction force, acceleration, and gravity. We will discuss this diagram together in class, as well.