Unit 2 Physics Area of Study 1 Motion

Area of Study 1 Ch 4 Aspects of Motion Chapter 5 Newton’s Laws

On completion of this chapter,  You will have covered material from the study of movement including:  vector techniques in two dimensions  forces in two dimensions  Newton's laws of motion  problems in mechanics including weight and friction. Area of Study 1 Ch 5 Newton’s Laws

Force as a vector  In this chapter we will consider the forces that cause motion to occur.  This branch of Physics is called mechanics and in particular – this section is called dynamics.  In simple terms; a force can be thought of as  a push or  a pull. Area of Study 1 Ch 5.1 Force as a vector

Force as a vector  Forces are fundamental to the nature of matter and the structure of the universe.  Consider each of the photographs in Figure 5.1 and identify each force - push or pull - that is acting. Area of Study 1 Ch 5.1 Force as a vector

Force as a vector  Figure 5.1 push or pull 5.1 Force as a vector

Force as a vector  Forces that act directly on a body are called contact forces  They require one object or material touching another because the body will only experience the force while contact is maintained.  Forces that act on a body at a distance are non-contact forces.  Gravitational, magnetic and electric forces are non-contact forces. 5.1 Force as a vector

Force as a vector  The action of a force is usually recognised through its effect on an object or body.  A force may do one or more of a number of things to the object. It may  change its shape,  change its speed or  change only the direction of its motion.  The tennis racquet in Figure 5.1a has applied a force to the tennis ball, and, as a consequence, the speed of the ball changes along with its direction. The ball also changes shape while the force acts! 5.1 Force as a vector

Force as a vector  The amount of force acting can be measured using the SI unit called the newton.  One newton (1 N) is defined as the force required to make a mass of 1 kg accelerate at 1 m s -­2.  The unit, honours Sir Isaac Newton ( ), who is still considered to be one of the most significant physicists to have lived.  A force of one newton, 1 N, is approximately the force you have to exert when holding a 100 g mass (a small apple) against the downward pull of gravity. 5.1 Force as a vector

Force as a vector  FORCE is a vector quantity.  It requires a magnitude and a direction to describe it fully.  In a diagram, a force is usually shown as an arrow whose length represents the magnitude of the force and whose direction is indicated by the arrow.  Consider the case of a soccer player who kicks the ball horizontally with a force of 95 N towards the east. 5.1 Force as a vector

Net Force  If more than one force acts on a body at the same time, the body behaves as if only one force—the vector sum of all the forces—is acting.  The vector sum of the forces is called the resultant or net force, ΣF (shown as a double-headed arrow).  The NET FORCE acting on a body experiencing a number of forces acting simultaneously is given by the vector sum of all the individual forces acting:  ΣF = F 1 + F 2 + … + F n 5.1 Force as a vector

Net Force  If the forces are acting at an angle to each other, the resultant force must still be found by performing a vector addition.  Consider the example of a shopping trolley that is being simultaneously pushed from behind by one person and pushed from the side by another.  This situation is illustrated in Figure Force as a vector

Net Force  If the forces are acting at an angle to each other, the resultant force must still be found by performing a vector addition.  Consider the example of a shopping trolley that is being simultaneously pushed from behind by one person and pushed from the side by another.  Force as a vector

Net Force  Consider the example of a shopping trolley that is being simultaneously pushed from behind by one person and pushed from the side by another.  Force as a vector

Vector Components  It is often helpful to divide a force acting in a two-dimensional plane into two vectors.  These two vectors are called the components of the force.  Consider, for example, the pulling force of 45 N acting on the cart shown in Figure 5.9.  This pulling force is acting through the rope and is known as tension or a tensile force.  It is usual to construct a right-angled triangle around the force vector. 5.1 Force as a vector

Vector Components Force as a vector