LEARNING OBJECTIVES

Knowledge & Understanding

- Explain what a force is. Describe everyday situations where forces act.
- Distinguish between gravitational mass, inertial mass and weight.
- Calculate the density of substances from their mass and volume.
- Distinguish between balanced and unbalanced forces.
- State Newton's three laws of motion and use them to solve problems (F = ma, W = mg).
- Describe experiments used to illustrate Newton's laws of motion.
- Identify examples of action–reaction forces.
- Explain what friction is and describe its effects. Solve problems involving friction.
- Explain the notion of drag force as a cause of terminal velocity .
- Describe the concept of torque and how it differs to force.

Scientific Techniques

- Determine how the acceleration of an object depends on its mass and the unbalanced force acting on it.
- Draw free-body and vector diagrams of applied forces.
- Examine graphically the result of forces on objects.
- Identify sources of errors in Newton’s Law experiments.
- Design simple experiments to test the ways of increasing or decreasing friction.
- Relate a knowledge of forces to car accidents and transport safety issues.

COMPLEX REASONING PROCESSES

- Solve problems involving Newton’s laws and frictional forces in more complex situations.
- Distinguish between relevant and irrelevant information in situations involving forces.
- Apply a knowledge of forces and torque to various sporting and mechanical situations.

- A force is a push or a pull exerted on a body.
- Newton's First Law states: An object maintains its state of rest or constant velocity motion unless it is acted on by an external unbalanced force.
- Inertia is the tendency of an object to resist a change to its motion.
- Newton's Second Law of motion: The acceleration of an object varies directly as the external unbalanced force applied to it and inversely proportional to its mass; i.e. F = ma.
- Newton's Third Law of motion states: To every action there is an equal and opposite reaction; or: if a body A exerts a force on another body B, then body B exerts an equal and opposite force on body A.
- The force of gravity on an object is the object's weight.
- Mass is a measure of the amount of substance in an object. It is related to weight by F
_{W}= mg. - When an object moves through a fluid, it experiences a frictional or drag force (F
_{f}). - When a body falls freely under gravity, it begins to accelerate at g (10 m s
^{-2}) but because of air resistance this value slowly decreases until it reaches zero. At this speed the object has reached terminal velocity. - Normal force is the force exerted on a body by a surface against which it is pressed. It is always perpendicular to the surface.
- The types of friction are limiting, sliding and rolling.
- The ratio of frictional force to the normal contact force is called the coefficient of
friction (µ); i.e. F
_{f}= µF_{N}.