Contact force

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Contact force
Contact force demonstration | Image: Force in Physics

A contact force is a type of force that occurs when two objects are physically in contact with each other. It results from the interaction between objects that are in direct contact, as opposed to non-contact forces, which operate between objects without physical contact.



Contact force example - kicking
When you kick a football, you apply force through direct contact | Image: Force in Physics

When a football player applies force with their leg to kick the football, a contact force arises as the football and the player’s leg come into direct contact. This contact force occurs due to the physical interaction between the objects at the moment of impact. It’s this contact force that enables the player to transfer energy to the football, propelling it forward and illustrating how contact forces involve the push or pull resulting from objects physically touching during an interaction.


Contact force example - throwing
Throwing a basketball involves force when your hand releases it | Image: Force in Physics

When a basketball player throws a basketball, a contact force comes into play. This force originates from the direct interaction between the player’s hand and the basketball. As the player exerts a push or pull on the ball, their hand physically touches the basketball’s surface, creating contact between the two objects. This contact force enables the player to transfer momentum and energy to the basketball, propelling it through the air. It exemplifies how contact forces facilitate actions involving physical touch and interaction between objects.


Contact force example - pushing
Pushing a toy car causes it to move through contact force between your hand and the car | Image: Force in Physics

When a small child plays with a toy car and applies force with their hand to set the car in motion, they are demonstrating a contact force. In this scenario, as the child’s hand pushes the car, it comes into physical contact with the car, resulting in the application of force. This contact force is essential for the child to impart motion to the car, highlighting how contact forces arise when two objects are in direct contact and influence their interactions, as seen in this example.


Contact force example - leaning
When you lean against a wall, your body exerts contact force on the wall | Image: Force in Physics

When a boy leans against a wall, a contact force is generated between his body and the wall. This contact force arises because the boy’s body is in direct contact with the wall. As he leans, his body applies a force to the wall, and in response, the wall exerts an equal and opposite force on his body. This interaction demonstrates contact forces, where objects in physical contact exert forces on each other, in this case, supporting the boy’s weight and preventing him from falling.


Contact force example - hitting
Hitting a billiard ball involves direct contact force from the cue | Image: Force in Physics

When a man aims to strike a billiard ball using a cue stick, he applies force to the ball through the stick. This action creates contact between the billiard ball and the cue stick, resulting in the generation of a contact force. Contact forces, exemplified in this scenario, arise when two objects – in this case, the cue stick and the billiard ball – come into direct physical contact, resulting in the application of force through their interaction.


Contact force example - pushing
You pull a wooden desk with contact force applied to the desk’s surface | Image: Force in Physics

In the scenario of pulling a wooden desk, a contact force comes into play. When the boy aims to move the wooden desk, he directly interacts with it by touching it with his hand. This physical contact between the boy’s hand and the wooden desk generates a contact force. Contact forces, exemplified here, occur when two objects – in this case, the wooden desk and the boy’s hand – come into direct contact, resulting in the application of force through their physical interaction. This force enables the boy to pull the desk, illustrating how contact forces are integral to actions involving physical touch between objects.


Contact force example - plucking
Plucking a mushroom applies force at its stem through contact | Image: Force in Physics

When a boy plucks a mushroom from the garden, contact force comes into play. As he exerts force with his hand to detach the mushroom, direct physical interaction occurs between his hand and the mushroom. This interaction leads to the application of a contact force between the two objects: the mushroom and his hand. The contact force in this case is what allows the boy to successfully pluck the mushroom, as it results from the direct contact between the objects involved in the action.


Contact force example - flipping
Flipping a page of a book is contact force with the page itself | Image: Force in Physics

When a boy flips the page of a book, contact forces are at play. His application of force through his hand onto the book’s page results in the page flipping. This force arises due to direct contact between his hand and the page, illustrating how contact forces occur when two objects, in this case, the page and the boy’s hand, physically interact, leading to the application of force through their direct touch, resulting in the page’s movement.


Contact force example - picking
Picking a ball from the floor involves contact force between your hand and the ball | Image: Force in Physics

As a small girl picks a ball from the floor, she exerts force using her hand. The action of picking involves direct physical contact between her hand and the ball. This contact leads to the emergence of a contact force between the two objects – the ball and her hand. Contact forces, as exemplified here, arise when two objects – in this case, the hand and the ball – come into direct physical contact, leading to the application of force through their interaction during the process of picking up the ball.


Muscular force

Contact force types - muscular force
Pushing a heavy stone requires muscular effort involving contact force | Image: Force in Physics

A boy is using muscular force to push a heavy stone. This force arises from the contraction of his muscles, especially in his hands, allowing him to exert the effort needed to move the stone. Muscular force, a type of contact force, is generated when muscles contract to create a push or pull, as shown in this scenario where the boy’s muscle strength propels the stone forward.


Contact force types - friction
Applying brakes to a bike involves contact force due to friction | Image: Force in Physics

When a person applies the brakes to a bike, friction becomes a crucial factor. As the brakes are engaged, the bike’s tires come into contact with the road surface and slide against it. This interaction generates a force known as friction, which acts to oppose the bike’s motion. Essentially, friction is the force that effectively stops the bike. It’s important to note that friction always acts in the direction opposite to the object’s motion, as demonstrated in this braking scenario.


Contact force types - tension
Using a rope to draw water from a well creates tension, a type of contact force | Image: Force in Physics

When a boy pulls a rope to draw water from a well, tension occurs in the rope. This tension arises because the rope is being pulled in opposite directions, with the boy pulling upward and the weight of the water-filled bucket pulling downward. Tension is the internal force within the rope that results from these opposing forces, leading the rope to resist being pulled apart.

Applied force

Contact force types - applied force
Stretching a rubber band involves the application of contact force to it | Image: Force in Physics

Applied force refers to the effort exerted on an object to make it move, change its speed, or alter its shape. For example, when you push a door to open it, your hand applies force to the door. Similarly, when you stretch a rubber band by pulling it with your fingers, you’re applying force to the rubber band. This concept helps us understand how external factors affect the behavior of objects in the world, whether in everyday activities or scientific experiments.

Normal force

Contact force types - normal force
A wooden chest resting on a horizontal surface experiences contact force known as normal force | Image: Force in Physics

When a wooden chest is placed on a floor, it experiences a perpendicular force exerted by the floor, which prevents it from falling through. This force, known as the normal force, acts perpendicular to the surface of the chest, supporting its weight and preventing it from sinking into the floor.


Contact force types - drag
A skydiver in freefall encounters contact force called drag | Image: Force in Physics

As a skydiver descends in freefall, they encounter an upward force exerted by the air, which opposes their downward motion. This opposing force, commonly known as air resistance or drag, acts in the opposite direction to the skydiver’s movement, slowing their descent and affecting their trajectory.

Mechanical force

Contact force types - mechanical force
Drilling a hole in a wall using a drill machine involves contact force known as mechanical force | Image: Force in Physics

Picture a man using a drill machine to create a hole in a wall. To accomplish this task, the drill machine generates a force necessary for the drill bit to penetrate the wall’s surface. This force, originating from the mechanical action of the machine, is precisely what we refer to as mechanical force.

Spring force

Contact force types - spring force
Using a clickable ballpoint pen relies on contact force from the spring | Image: Force in Physics

When pressure is applied to a clickable ballpoint pen, a force is produced as the pen’s internal spring gets compressed. This force, resulting from the spring’s compression, leads to the extension of the pen’s point and is commonly referred to as spring force.


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