What is a force? A force is a push, pull or twist.
Say if the following are pushes, pulls or twists: Writing on paper Typing on a keyboard Tug-of-war Unscrewing the top off a bottle Posting a letter through a door Putting on a pair of socks Turning a door handle Push Push Pull Twist Twist Push Pull Twist Twist
Types of force you need to know…… Gravity Friction Air resistance Magnetism Tension Electrostatic Nuclear Compression
Describing the forces The force you get when two material rub together The force you get when a material is being stretched The force you get when a material is being squashed The force that enables compasses to work Magnetism Friction Compression Tension
Describing the forces Gravity Nuclear Air resistance Electrostatic The force that holds the particles in a nucleus together The force you get when an object moves through air The force that exists between all objects with mass The force you get between two charged objects
Attractive or repulsive? Gravity? Magnetism? Electrostatic? Attractive, always Attractive and repulsive Attractive and repulsive
Contact and non-contact If two objects or materials need to be touching for the force to have an effect then it is a C________ force. Examples: If two objects or materials do not need to be t______ for the force to have an effect then it is a NON CONTACT force. Examples: ONTACT Friction Airresistance ouching Gravity Electrostatic Magnetic
Gravity Gravity is an attractive f____ that exists between all m_____. Gravity is always a_______. The l____ the mass is, the greater the gravitational attraction. The f_____ away a mass is, the less the gravitational attraction. Your w____ is the pull of the Earth’s gravity on your body. If you stood on the M___ you would weigh less than on Earth. This is because the Moon has less mass than Earth, so the Moon’s g_________ pull is weaker than the Earth’s. orce asses ttractive arger urther eight The Moon is kept in orbit around the Earth due to gravity. oon ravitational
Mass = 10kg 10kg Weight = 100 N Mass and weight What is the difference between mass and weight? Your mass is a measure of how many particles there are in your body. It does not matter where you are in the Universe, your mass does not change. Your weight is a measure of the pull of gravity on your body. Your weight depends upon what planet you are standing on. You would weigh less on Mercury than on Earth because Mercury is smaller than Earth. What is mass measured in? Kilograms What is weight measured in? Newtons
Draw a force diagram for a falling object when it first starts to fall. Air resistance Weight Force diagrams Force diagrams show you the direction a force is acting in. It shows you the direction an object is being pushed, pulled or twisted. The direction of the arrow shows you the direction of the force. The sizes of the arrows can be used to compare the sizes of the forces.
Unused homework diary on a table What force pulls down on the book? Gravity The diary does not move, so there must be an equal and opposite force pushing up on the diary. What do we call this force? Reaction force
Forces on a speeding fish? What is thrust? A forward push What is upthrust? The upwards force on a body in a liquid or a gas Upthrust Friction Thrust Weight
Label the forces acting on the moving ship shown: Upthrust or buoyancy Air resistance Thrust Friction Weight
A ship arrives at port and is loaded with cargo: What happens to the weight of the ship? What happens to the upthrust on the ship? Which is the largest force, weight or upthrust? Increases Increases Both equal
Forces and motion If an object is stationary and an unbalanced force acts on it, it will start to move. If an object is moving and an unbalanced force acts on it there are three possibilities… The object could speed up. The object could slow down. The object could change direction.
In which direction, if any will the following stationery objects move?
What is friction? If you rub your hands together there is resistance to the motion. What do we call this force? Friction What causes it? Even though your hands look smooth, on a microscopic level it is not, so when your hands rub together you get the resistive force of friction.
Direction of friction Friction always acts in the opposite direction to the way an object is moving. For the following moving objects, mark with an arrow, the direction friction is acting in.
Friction effects Friction always acts in the o______ direction to which an object is moving in. Friction is a type of f____. Whenever you get friction between two objects you always get h___ and w_____. You can reduce the effect of friction by using a l______. O_ is a lubricant used in car engines to reduce friction effects. pposite orce eat earing ubricant il
Starting moving… An object will only start to move if the forces applied to it overcome any frictional forces. For the examples shown say if the stationary objects will move or not, and if they do move, say in which direction.
Friction - useful or hindrance? Write down three instances where friction is useful and three where it is a hindrance. Discuss your ideas with the class and then have a vote on what the class thinks are the top three for each.
Heat Gravity Tension Friction Which of the following is not a force?
A. B.C. D. For a man standing up, in which direction does gravity act?
For a fish in water, what do we call force Z? • Friction • Air resistance • Gravity • Upthrust Z
Joules Metres Newtons Seconds In what units is force measured in?
Clock Voltmeter Joulemeter Newtonmeter What device is used to measure force?