1 Forces and Motion: Forces, Movement, Shape and momentum Flashcards
1.11 describe the effects of forces between bodies such as changes in speed, shape or direction
A force 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
1.12 identify different types of force such as gravitational or electrostatic
- Push or pull
- Frictional force
- Buoyancy force (upthrust)
- Gravitational force (weight)
- Magnetic force
- Electrostatic force
1.13 understand how vector quantities differ from scalar quantities
Scalar: quantities that can be defined by their magnitude (or size) alone
Vector: quantities where a direction is important too
1.14 understand that force is a vector quantity
force is a vector quantity!
1.15 calculate the resultant force of forces that act along a line
If in the same direction: add them together
If in opposite directions: Take smaller force from bigger => this number is the force just in the bigger force direction
1.16 know that friction is a force that opposes motion
friction is a force that opposes motion!
Frictional force between two surfaces is proportional to the force pressing them together.
does not depend on area
1.17 know and use the relationship between unbalanced force, mass and acceleration:
force = mass × acceleration
F=m×a
1.18 know and use the relationship between weight, mass and gravitational field strength:
weight = mass × gravitational field strength
W=m×g
1.19 know that the stopping distance of a vehicle is made up of…
stopping distance = thinking distance + braking distance
1.20 describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time
Thinking:
- How fast you’re going => faster you go, further you go
- Your reaction time => affected by old age; inexperience, tiredness, drugs, alcohol
Braking:
- How fast you’re going => faster you go, further you go
- Mass of vehicle => larger mass, longer it takes to stop
- How good the brakes are
- How good the grip is => depends on: road surface, weather conditions, tires
1.21 describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity)
When an object falls through a liquid or gas, the two main forces acting on it are the force if gravity (weight) acting downwards, and a frictional force acting upwards
As an object starts to fall, drag force = 0
As object picks up speed, drag force increases
Terminal velocity, drag force = weight
1.22 practical: investigate how extension varies with applied force for helical springs, metal wires and rubber bands
Helical spring
• A-B, spring stretches uniformly (loading)
•At B, spring exceeds elastic limit, spring no longer stretches uniformly
•If force is gradually reduced it follows dotted line (unloading)
•When the force reaches zero again the spring has a permanent stretch (AE)
Metal wires • A-B, wire stretches elastically • At B it begins to yield •B-C, wire yields and exhibits plastic flow. wire no longer stretches uniformly • at C wire breaks
Rubber bands
• easy to stretch at first
• eventually as force increases the band doesn’t get longer
• extension and force never proportional
•unloading curve doesn’t follow loading curve but no permanent stretch
1.23 know that the initial linear region of a force-extension graph is associated with Hooke’s law
A-B follows Hooke’s Law:
F = kx
F=force, K=springconstant, x=extension
1.24 describe elastic behaviour as the ability of a material to recover its original shape after the forces causing deformation have been removed
A spring and wire return to their original lengths when the force is removed
Rubber band is not elastic (curves don’t match)
There is some energy loss as an elastic band is stretched, no energy loss when a spring is stretched
