3&4 Describing motion & Forces

Question 1

Newtonian equations of motion

Answer 1

1. Vf = Vi + a∆t
2. Xf = Xi + Vi∆t + 1/2a(∆t)^2
3. Vf^2 = Vi^2 = 2a∆x
4. Xf - Xi = 1/2(Vi + Vf)∆t

Question 2

What is centripetal acceleration

Answer 2

• occurs in uniform circular motions
• Constant magnitude of velocity - but since direction changes, the acceleration also changes direction (always points towards the centre of the circle)

Question 3

Describe the differences in projectile motion

Answer 3

• horizontal acceleration is 0

* vertical acceleration is downward

Question 4

What are the properties of forces

Answer 4

• force is a vector - having both magnitude and direction
• forces are paired - two interacting objects exert a force on each other simultaneously
• force is additive - addition of forces = net force

Question 5

What is the SI unit of a newton?

Answer 5

1N = 1kg.m/s^2

Question 6

What are the two main types of forces?

Answer 6

Contact forces
• requires physical contact between the 2 interacting objects

Non-contact forces
• do not require contact, and acts over a distance
• may be short or long range
• also called field forces

Question 7

What are the 4 fundamental contact free forces and examples

Answer 7

1. gravity
   • binds solar system (rlly long range)
2. electromagnetic
   •binds atoms (long range)
3. the weak force
   • radioactive decay (rlly short range)
4. the strong force
   • binds nuclei (short range), keeps protons and neutrons together

Question 8

What are the main contact forces?

Answer 8

• tension forces
• normal forces
• friction forces
• spring forces

Question 9

What is newton’s law of universal gravitation?

Answer 9

There exists an attractive force between two objects proportional to the product of their masses and inversely proportional to the square of the distance between them
F= G(m1.m2)/r^2

Question 10

What is Coulomb’s law?

Answer 10

there exists an electric force between two charged objects proportional to the product of the magnitude of their charges and inversely proportional to the square of the distance between them

F= k(q1.q2)/r^2

Question 11

What is the normal force?

Answer 11

A contact force that the surface of an object exerts perpendicularly on an object that is pressing against the surface

Question 12

Friction on smoother surfaces

Answer 12

• As surfaces become smoother, the number of contact points increase and contact surface area increases.
• results in an increase in friction force between 2 objects

Question 13

What is static friction

Answer 13

The force that prevents objects from moving with respect to a contacting surface, and allows them to maintain their stationary status

Question 14

What happens at the maximum possible value of static friction

Answer 14

• applies when the object is sliding

* magnitude of the kinetic friction force is approximately constant while the object is sliding

Question 15

What is Hooke’s law?

Answer 15

Fs = -kx

• x is the change in length of spring from ints unstretched length, and k is the spring constant