1. Home
  2. College physics
  3. Dynamics: force and newton's
  4. Normal, tension, and other

4.5 Normal, tension, and other examples of forces  (Page 7/10)

<< Chapter < Page
  College physics     Page 7 / 10
Chapter >> Page >

All the forces discussed in this section are real forces, but there are a number of other real forces, such as lift and thrust, that are not discussed in this section. They are more specialized, and it is not necessary to discuss every type of force. It is natural, however, to ask where the basic simplicity we seek to find in physics is in the long list of forces. Are some more basic than others? Are some different manifestations of the same underlying force? The answer to both questions is yes, as will be seen in the next (extended) section and in the treatment of modern physics later in the text.

Phet explorations: forces in 1 dimension

Explore the forces at work when you try to push a filing cabinet. Create an applied force and see the resulting friction force and total force acting on the cabinet. Charts show the forces, position, velocity, and acceleration vs. time. View a free-body diagram of all the forces (including gravitational and normal forces).

Forces in 1 Dimension

Section summary

  • When objects rest on a surface, the surface applies a force to the object that supports the weight of the object. This supporting force acts perpendicular to and away from the surface. It is called a normal force, N size 12{N} {} .
  • When objects rest on a non-accelerating horizontal surface, the magnitude of the normal force is equal to the weight of the object:

    N = mg size 12{N= ital "mg"} {} .

  • When objects rest on an inclined plane that makes an angle θ size 12{θ} {} with the horizontal surface, the weight of the object can be resolved into components that act perpendicular ( w ⊥ ) and parallel ( w ∥ size 12{w rSub { size 8{ \lline \lline } } } {} ) to the surface of the plane. These components can be calculated using:

    w ∥ = w sin ( θ ) = mg sin ( θ ) size 12{w rSub { size 8{ \lline \lline } } =w"sin" \( θ \) = ital "mg""sin" \( θ \) } {}
    w ⊥ = w cos ( θ ) = mg cos ( θ ) size 12{w rSub { size 8{ ortho } } =w"cos" \( θ \) = ital "mg""cos" \( θ \) } {} .

  • The pulling force that acts along a stretched flexible connector, such as a rope or cable, is called tension, T size 12{T} {} . When a rope supports the weight of an object that is at rest, the tension in the rope is equal to the weight of the object:

    T = mg size 12{T= ital "mg"} {} .

  • In any inertial frame of reference (one that is not accelerated or rotated), Newton’s laws have the simple forms given in this chapter and all forces are real forces having a physical origin.

Conceptual questions

If a leg is suspended by a traction setup as shown in [link] , what is the tension in the rope?

Diagram of a leg in traction.
A leg is suspended by a traction system in which wires are used to transmit forces. Frictionless pulleys change the direction of the force T without changing its magnitude.
Got questions? Get instant answers now!

In a traction setup for a broken bone, with pulleys and rope available, how might we be able to increase the force along the tibia using the same weight? (See [link] .) (Note that the tibia is the shin bone shown in this image.)

Got questions? Get instant answers now!

Problem exercises

Two teams of nine members each engage in a tug of war. Each of the first team’s members has an average mass of 68 kg and exerts an average force of 1350 N horizontally. Each of the second team’s members has an average mass of 73 kg and exerts an average force of 1365 N horizontally. (a) What is magnitude of the acceleration of the two teams? (b) What is the tension in the section of rope between the teams?

  1. 0. 11 m/s 2 size 12{0 "." "11 m/s" rSup { size 8{2} } } {}
  2. 1 . 2 × 10 4 N size 12{1 "." 2 times "10" rSup { size 8{4} } " N"} {}
Got questions? Get instant answers now!

What force does a trampoline have to apply to a 45.0-kg gymnast to accelerate her straight up at 7 . 50 m/s 2 size 12{7 "." "50 m/s" rSup { size 8{2} } } {} ? Note that the answer is independent of the velocity of the gymnast—she can be moving either up or down, or be stationary.

Got questions? Get instant answers now!

(a) Calculate the tension in a vertical strand of spider web if a spider of mass 8 . 00 × 10 − 5 kg size 12{8 "." "00" times "10" rSup { size 8{ - 5} } " kg"} {} hangs motionless on it. (b) Calculate the tension in a horizontal strand of spider web if the same spider sits motionless in the middle of it much like the tightrope walker in [link] . The strand sags at an angle of 12º size 12{"12"°} {} below the horizontal. Compare this with the tension in the vertical strand (find their ratio).

(a) 7 . 84 × 10 -4 N size 12{7 "." "84" times "10" rSup { size 8{4} } " N"} {}

(b) 1 . 89 × 10 –3 N size 12{1 "." "89" times "10" rSup { size 8{"–3"} } " N"} {} . This is 2.41 times the tension in the vertical strand.

Got questions? Get instant answers now!

Suppose a 60.0-kg gymnast climbs a rope. (a) What is the tension in the rope if he climbs at a constant speed? (b) What is the tension in the rope if he accelerates upward at a rate of 1 . 50 m/s 2 size 12{1 "." "50 m/s" rSup { size 8{2} } } {} ?

Got questions? Get instant answers now!

Show that, as stated in the text, a force F ⊥ size 12{F rSub { size 8{ ortho } } } {} exerted on a flexible medium at its center and perpendicular to its length (such as on the tightrope wire in [link] ) gives rise to a tension of magnitude T = F ⊥ 2 sin ( θ ) size 12{T= { {F rSub { size 8{ ortho } } } over {2"sin" \( θ \) } } } {} .

Newton’s second law applied in vertical direction gives

F y = F − 2 T sin θ = 0 size 12{F rSub { size 8{y} } =F - 2T" sin "θ=0} {}
F = 2 T sin θ size 12{F rSub { size 8{ ortho } } =2"T sin "θ} {}
T = F 2 sin θ size 12{T= { {F rSub { size 8{ ortho } } } over {"2 sin "θ} } } {} .

Got questions? Get instant answers now!

Consider the baby being weighed in [link] . (a) What is the mass of the child and basket if a scale reading of 55 N is observed? (b) What is the tension T 1 size 12{T rSub { size 8{1} } } {} in the cord attaching the baby to the scale? (c) What is the tension T 2 size 12{T rSub { size 8{2} } } {} in the cord attaching the scale to the ceiling, if the scale has a mass of 0.500 kg? (d) Draw a sketch of the situation indicating the system of interest used to solve each part. The masses of the cords are negligible.

Got questions? Get instant answers now!
A vertical spring scale measuring the weight of a baby is shown. The scale is hung from the ceiling by a cord. The weight W of the baby is shown by a vector arrow acting downward and tension T sub one acting in the cord is shown by an arrow upward. The tension in the cord T sub two attached to the ceiling is represented by an arrow upward from the spring scale and downward from the ceiling.
A baby is weighed using a spring scale.

Questions & Answers

what does preconceived mean
sammie Reply
physiological Psychology
Nwosu Reply
How can I develope my cognitive domain
Amanyire Reply
why is communication effective
Dakolo Reply
Communication is effective because it allows individuals to share ideas, thoughts, and information with others.
effective communication can lead to improved outcomes in various settings, including personal relationships, business environments, and educational settings. By communicating effectively, individuals can negotiate effectively, solve problems collaboratively, and work towards common goals.
it starts up serve and return practice/assessments.it helps find voice talking therapy also assessments through relaxed conversation.
miss
Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment
Wekolamo Reply
please i need answer
Wekolamo
because it helps many people around the world to understand how to interact with other people and understand them well, for example at work (job).
Manix Reply
Agreed 👍 There are many parts of our brains and behaviors, we really need to get to know. Blessings for everyone and happy Sunday!
ARC
A child is a member of community not society elucidate ?
JESSY Reply
Isn't practices worldwide, be it psychology, be it science. isn't much just a false belief of control over something the mind cannot truly comprehend?
Simon Reply
compare and contrast skinner's perspective on personality development on freud
namakula Reply
Skinner skipped the whole unconscious phenomenon and rather emphasized on classical conditioning
war
explain how nature and nurture affect the development and later the productivity of an individual.
Amesalu Reply
nature is an hereditary factor while nurture is an environmental factor which constitute an individual personality. so if an individual's parent has a deviant behavior and was also brought up in an deviant environment, observation of the behavior and the inborn trait we make the individual deviant.
Samuel
I am taking this course because I am hoping that I could somehow learn more about my chosen field of interest and due to the fact that being a PsyD really ignites my passion as an individual the more I hope to learn about developing and literally explore the complexity of my critical thinking skills
Zyryn Reply
good👍
Jonathan
and having a good philosophy of the world is like a sandwich and a peanut butter 👍
Jonathan
generally amnesi how long yrs memory loss
Kelu Reply
interpersonal relationships
Abdulfatai Reply
What would be the best educational aid(s) for gifted kids/savants?
Heidi Reply
treat them normal, if they want help then give them. that will make everyone happy
Saurabh
What are the treatment for autism?
Magret Reply
hello. autism is a umbrella term. autistic kids have different disorder overlapping. for example. a kid may show symptoms of ADHD and also learning disabilities. before treatment please make sure the kid doesn't have physical disabilities like hearing..vision..speech problem. sometimes these
Jharna
continue.. sometimes due to these physical problems..the diagnosis may be misdiagnosed. treatment for autism. well it depends on the severity. since autistic kids have problems in communicating and adopting to the environment.. it's best to expose the child in situations where the child
Jharna
child interact with other kids under doc supervision. play therapy. speech therapy. Engaging in different activities that activate most parts of the brain.. like drawing..painting. matching color board game. string and beads game. the more you interact with the child the more effective
Jharna
results you'll get.. please consult a therapist to know what suits best on your child. and last as a parent. I know sometimes it's overwhelming to guide a special kid. but trust the process and be strong and patient as a parent.
Jharna
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
<< Chapter < Page Page > Chapter >>
Practice Key Terms 3

Read also:

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics' conversation and receive update notifications?

Ask