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### Scientific and Engineering Practices

Developing and Using Models

### Crosscutting Concepts

Systems and System Models

### Knowledge

Students know:
• An object will remain at rest or in uniform motion unless acted on by an outside force.
• The velocity of an object changes when it is subjected to an external force.
• Gravity's acceleration is different on different planets.
• Air resistance is responsible for terminal velocity for objects in free fall.
• The property of inertia as related to mass.
• Forces must be unbalanced for an object to change its motion.
• Friction is a force that opposes motion.

### Skills

Students are able to:
• Organize data that represent the net force on an object (mass and acceleration) via tables and graphs.
• Construct force diagrams that identify all external forces acting on the system.
• Explain (conceptually and mathematically) the relationship between force, mass, and acceleration. (The greater the force on an object, the greater its change in motion but the same amount of force applied to an object with more mass will result in less acceleration.)
• Relate the difference between mass and weight. (Weight is a force dependent upon acceleration and mass is constant regardless of acceleration.)
• Calculate weight when given mass. (Fg=mg)
• Explain acceleration due to gravity as an example of uniformly changing velocity. (g=9.8 m/s2)
• Relate the presence of air resistance to the concept of terminal velocity of an object in free fall.
• Identify friction as a force that opposes motion of an object.
• Classify the frictional forces present in different situations. (Sofa resting on the floor is static friction. A box pushed across the floor is sliding friction. A ball rolling across the floor is rolling friction. A boat moving through a river is fluid friction. An object in free-fall is fluid friction.)
• Explain the property of inertia as related to mass. (An object at rest or at constant speed in a straight line will remain in that state unless acted upon by a force causing an unbalanced net force.)
• Explain balanced and unbalanced forces mathematically and graphically with respect to acceleration to establish the relationship between net force, acceleration, and mass.

### Understanding

Students understand that:
• The motion of a system may be predicted by applying Newton's laws of motion to force diagrams that identify all external forces acting on the system.
• Forces acting on an object affect the motion of that object.

### Vocabulary

• Weight
• Mass
• Gravity
• Acceleration
• Velocity
• Terminal velocity
• Free fall
• Friction
• Static friction
• Rolling friction
• Fluid friction
• Inertia
• Force
• Balanced forces
• Unbalanced forces
• Net force
• Action-reaction pairs
• Vectors