Forces And Motion Flashcards
How can you measure force?
Using a Newton balance or a spring balance
What force always opposes motion?
Friction
How can friction be reduced?
give some examples too
By keeping he moving surfaces apart?
Example: lubrication (e.g. Oil), cushion or air (e.g. Hovercraft)
A force is something that can:
- Start or stop an object moving
- Speed up or slow down a moving object
- Change the direction in which an object is moving
- Make an object rotate
- Change the shape of an object
What unit is force measured in?
Is force weight/mass?
Newtons (N)
Force is weight NOT MASS
How can you find the weight of an object if you know it’s mass?
Multiply it’s mass by 10 (more precisely 9.8)
The frictional force between two surfaces is proportional to ???
The force pressing them together
What page are you about to go to in the revision booklet to revise elastic limit etc
Page 4 and 5
What is the resistive force (approximately) equal to?
The speed squared
What is the drag force when the object STARTS to fall?
The drag force is zero
When is terminal velocity reached?
When the drag force is equal to the weight
What is the stopping distance?
The thinking distance (distance travelled while thinking about braking) + the braking distance (distance travelled one the brakes have been applied)
What is thinking distance proportional to?
The speed
What does reaction time depend on?
Age, eyesight, tiredness, alcohol, drugs, medication, etc
The braking distance will be larger if:
- The speed is higher
- The braking force is smaller
- The mass of the at is larger
How does a helical steel spring stretch between A and B?
Uniformly
What happens at B for a helical steel spring?
It reaches it’s elastic limit and the extensions become much larger
When a helical steel spring has been unloaded after passing its elastic limit what happens to it?
It has a permanent stretch
How does a copper wire stretch between A and B?
Uniformly
Elastically
What does it mean when something is described as elastic?
When the unloading line matches the loading line
What happens between B and C to a copper wire?
The wire yields and exhibits plastic flow
The extension become much larger
What is a vector quantity and give 6 examples
A quantity where direction is important, its not just about magnitude.
Displacement, velocity, momentum, acceleration, force, weight
Relationship between momentum, mass and velocity
momentum = mass x velocity
What is the big rule of momentum and what is it called
Momentum is conserved - the Principle of Conservation of Momentum
