Topic 6 - Forces and motion Flashcards
What are the 10 types of forces? (10)
- Electric
- Tension
- Compression
- Thrust
- Weight
- Lift
- Friction (incl. drag)
- Contact
- Upthrust
- Magnetic
What is the definition for electric?
Attraction or repulsion between two charged objects.
What is the definition for tension?
Occurs within materials/objects when stretched eg in a string suspending an object.
What is the definition for thrust?
A force which propels an object forward – usually refers to forward force generated by engines.
What is the definition for weight?
Force acting on a mass due to the effect of a gravitational field.
What is the definition for lift?
An upwards force generated by the wing of an aircraft when there is a difference in pressure above and below the wing.
What is the definition for friction?
A force which opposes the motion of an object.
What is the definition for contact?
A force which occurs whenever an object rests on something else, and which always acts at 90 degrees to the surface where it rests.
What is the definition for upthrust?
The force which enables objects to float due to the displacement of fluid.
What is the definition for Magnetic?
Attraction or repulsion due to magnetic fields.
balanced forces?
When no force acts on an object, or the forces on the object are balanced. (ie they cancel each other out), the object will either remain stationary, or if it is already moving, it will continue to move at a constant speed.
Unbalanced forces?
If the forces on an object do not cancel each other out, then they are said to be unbalanced . The unbalanced force is also sometimes referred to as an overall force, a net force or a resultant force.
Newton’s 1st law?
When the forces acting on an object are balanced
there is no effect on the motion of the object.
Newton’s 2ed law?
When the forces on an object are unbalanced there is a resultant force and this will cause an acceleration (or a deceleration).
Newton’s 3ed law?
When two objects interact they exert forces on each other which are equal and opposite.
A force of friction acts: (2)
- when an object moves through a fluid (e.g. air or water)
- or when solid surfaces slide (or tend to slide) across each other.
When a body falls: (3)
- initially it accelerates due to the force of gravity.
- Frictional forces increase until they balance the gravitational forces
- the resultant force eventually reaches zero and the body falls at its terminal velocity.
The greater the speed of a vehicle: (2)
- the greater the braking force needed to stop it in a certain distance;
- the greater the distance needed to stop it with a certain braking force.
The stopping distance of a vehicle depends on: (2)
- the distance the vehicle travels during the driver’s reaction time;
- the distance the vehicle travels under the braking force.
The overall stopping distance is greater if: (5)
- the vehicle is initially travelling faster;
- the driver’s reactions are slower (due to tiredness, drugs, alcohol);
- there are adverse weather conditions (wet/icy roads, poor visibility);
- the vehicle is poorly maintained (e.g. worn brakes/tyres);
- the vehicle is heavier.
Stopping distance?
Stopping distance = thinking distance + braking distance
- Thinking distance
is the distance a vehicle travels in the time it takes for the driver to apply the brakes after realising they need to stop
- Braking distance
is the distance a vehicle travels in the time after the driver has applied the brake
Hooke’s law? (2)
Robert Hooke (1635 - 1703) said that when a spring is stretched, its extension is directly proportional to the load.
This is true below the elastic limit which is the point at which the spring is permanently deformed.
