Forces, movement, shape and momentum Flashcards
What effect does a force have on an object?
- Changes object’s speed
- Changes object’s direction
- Changes object’s shape
List the different types of forces?
- Gravitational
- Electrostatic
- Weight
- Normal reaction
- Friction
- Air resistance
- Upthrust
- Nuclear
- Magnetic
What is the difference between scalar and vector?
- Scalar - magnitude only
- Vector - magnitude and direction
name 6 vector quantities?
There are only 6 vector quantities (assume everything else is scalar!)
- Displacement
- Velocity
- Acceleration
- Force
- Weight
- Momentum
What is Newton’s 1st Law?
- If forces acting on an object are balanced, the resultant force is zero
- Object at rest, stays stationary
- Object moving, continues to move in same direction and at same speed
What is Newton’s 2nd Law?
- Acceleration is proportional to resultant force
- Inversely proportional to mass of object
How to calculate resultant force acting along a line
Add up all forces acting in useful direction
- Subtract all forces acting in the opposite direction
equation for force, mass and acceleration?
Force = mass x acceleration F = m x a
equation for Weight , mass, and ravitational field strength
Weight = mass x gravitational field strength W = m x g
equation for stopping distance?
Stopping distance = thinking distance + braking distance
Define stopping distance
- The distance travelled by a vehicle after a hazard has been spotted until it comes to a
complete rest - Stopping distance = thinking distance + braking distance
What factors affect braking distance?
- Speed vehicle is travelling
- Mass of vehicle
- Condition of road
- Tyres and brakes
How is braking distance increased?
- If vehicle is travelling at higher speed
- Worn brakes
- Icy road
What factors affect thinking distance?
- Reaction time
- Tiredness
- Drink and drugs
How is thinking distance increased?
- Tiredness
- Driving under the influence of drink and drugs
Describe the process of terminal velocity
- Weight acts downwards
- Drag acts upwards
- Object accelerates downwards
- Eventually weight = drag
- No resultant force, no acceleration, forces are balanced
- Terminal velocity (constant velocity) is reached
What is Hooke’s law?
- The extension of a spring is directly proportional to the force applied, provided its limit
of proportionality is not exceeded
Define elastic behaviour
- The ability of a material to revert to its original shape after the forces causing deformation
have been removed
What happens if elastic limit is exceeded?
- Material will no longer revert to original shape after the forces have been removed
What is the equation for momentum?
- Momentum = mass x velocity
p = m x v
What is the unit of momentum?
- kg m/s
Explain how seat belts/crumple zones/air bags prevent serious injury
- Same momentum change
- But time of impact increases
- Reducing force felt
- Seat belt stretches increasing area over which force acts
- Pressure on body reduces
When 2 vehicles collide what happens
- They exert equal and opposite forces on each other
- Their total momentum is unchanged
equation for force, change in momentum and time?
Force = change in momentum
Time
F = (mv - mu)
t
What is Newton’s 3rd Law?
- Two objects exert equal and opposite forces on each other
What is a moment?
- The turning effect of a force
equation for moment?
Moment = force x perpendicular distance from pivot
How do you increase the moment of a force?
- Increase distance
- Increase force
Define ‘centre of mass’
The point where the mass appears to be concentrated
