Physics 10th Class: Forces and Motion

Force and Resultant Forces

• A force is a push or a pull that can change the motion of an object.
• Forces are measured in Newtons (N).
• Several forces can act on an object at the same time.
• The resultant force is the single force that has the same effect as all the forces acting together.
• If the forces are balanced, the resultant force is zero, and the object will either stay still or continue moving at a constant speed in a straight line.
• If the forces are unbalanced, the resultant force is not zero, and the object's motion will change. This change could be a change in speed or direction.

Friction

• Friction is a force that opposes motion between two surfaces that are in contact.
• Friction always acts in the opposite direction to the motion.
• Friction is a necessary force in many situations. For example, it allows us to walk without slipping, and it slows down cars when the brakes are applied.
• The amount of friction depends on the nature of the surfaces in contact and the force pressing them together.
• Rough surfaces generally produce more friction than smooth surfaces.
• A larger force pressing the surfaces together usually produces more friction.

Types of Friction

• Static friction: This is the force that prevents an object from moving when a force is applied to it. To start moving an object, you must apply a force strong enough to overcome static friction.
• Sliding friction: This is the force that opposes the motion of an object sliding over a surface. Sliding friction tends to be less than static friction between the same surfaces.
• Rolling friction: This is the force that opposes the motion of a rolling object. Rolling friction is generally much smaller than sliding friction between the same surfaces. Rolling on wheels helps reduce friction significantly compared to sliding or dragging.
• Fluid friction: This is the force that opposes the motion of an object moving through a liquid or a gas. Examples include air resistance (a type of fluid friction) and water resistance. The faster an object moves through a fluid, the greater the fluid friction. Air resistance increases as the speed of the object increases.