# 3.2 Forces in Action Flashcards Preview

## Physics A Level > 3.2 Forces in Action > Flashcards

Flashcards in 3.2 Forces in Action Deck (27)
1
Q

What is a force? (2)

A

An interaction between two objects involving a push or pull

A vector with direction in space

2
Q

What are the four fundamental forces? (4)

A

Gravitational
Electromagnetic
Strong nuclear
Weak nuclear

3
Q

What force acts on an object in water, allowing it to float?

A

Upthrust

4
Q

What force acts on an object when it is pulled by a string?

A

Tension

5
Q

What force acts between a surface and an object when they are in contact with each other?

A

Normal contact force

6
Q

What is friction?

A

Particles colliding with a moving object, causing kinetic energy to be lost as thermal energy

7
Q

What is a free body diagram?

A

A diagram using a dot to represent an object and arrows to scale to show the direction and magnitude of the forces acting on it

8
Q

What is a plumb line?

A

A mass suspended by a length of string, allowing straight, vertical lines to be drawn

9
Q

How is the centre of mass of a 2D object found? (4)

A

Choose a point on the object and allow it to swing freely from a pin before coming to rest
Using a plumb line, draw a vertical line through the pin
Repeat this twice more, creating a point where all three lines cross
The point where they cross is the centre of mass

10
Q

What is drag?

A

The frictional force experienced by an object travelling through a fluid

11
Q

What factors affect drag? (5)

A
```Speed of the object
Cross-sectional area
Shape of the object
Roughness/texture of the object
Density of the fluid that is travelled through```
12
Q

How is drag force and speed linked?

A

Drag force is proportional to speed^2

13
Q

What are the forces on an object in the instant that it falls? (2)

A

No drag

Weight (acceleration = g)

14
Q

What happens as a falling object’s speed increases? (2)

A

Drag force increases

Instantaneous acceleration decreases (less than g)

15
Q

What happens when an object reaches terminal velocity? (2)

A

Drag is equal and opposite to weight

Acceleration is zero so speed is constant

16
Q

What is the moment of a force?

A

The turning effect of a force about a pivot

Moment = force x perpendicular distance from pivot

17
Q

What is a couple?

A

A pair of equal but opposite forces acting parallel and on different lines
They cause a turning effect but no translational movement

18
Q

What is the torque of a couple? (2)

A

The moment of a couple

Torque = one of the forces x perpendicular distance between forces

19
Q

What is the principle of moments? (2)

A

When a body is in equilibrium, the net force acting on it is zero and its net moment is zero
The sum of clockwise moments = the sum of anti-clockwise moments

20
Q

What is the centre of gravity?

A

The point at which the entire weight of the object can be said to act

21
Q

What is the difference between a torque and a moment?

A

A moment can have a non-zero resultant force, thereby causing movement whereas a torque always has a resultant force of zero

22
Q

What is density? (2)

A

Mass per unit volume

Density = mass / volume

23
Q

What is pressure? (2)

A

Force per unit area (acting perpendicular to the surface)

Pressure = force / area

24
Q

What is the difference between solid and liquid pressure? (2)

A

Solid pressure - the smaller the area, the higher the pressure
Liquid pressure - in a fluid at rest, pressure at any point acts equally in all directions and increases with depth

25
Q

What is Archimedes’ Principle?

A

The upthrust that a floating or submerged object feels is equal to the weight of displaced fluid

26
Q

How is the upthrust on an object in a fluid calculated?

A

Pressure = height of liquid above x density of liquid x acceleration due to gravity

27
Q

How is the density of an object calculated? (2)

A

Use a Eureka can - volume of water displaced = volume of object
Use a balance to find the mass of the object