Forces revision (junior) In discussing forces we have come across the following terms: - balanced - unbalanced - contact - non-contact - net force - zero net force Now let's see if we can apply these terms to real-life situations. Consider the video on the right. How do we know a force is acting between the two magnets? one of the magnets changes shape one of the magnets changes speed There is a net zero an unbalanced a contact a balanced force acting on the magnet. Consider the video on the right. A globe is floating in mid-air. Amazing. What forces do you think might be acting on the floating object? drag and thrust gravity and magnetic repulsion gravity and drag thrust and gravity These forces are examples of balanced, non-contact unbalanced, contact balanced, contact forces acting on the object. Consider the picture of the vehicle parked on the right. What can you say about the forces acting on the vehicle? The two forces acting on the vehicle are both acting in a downward direction. The forces are non-contact and unbalanced There is zero net force acting on the vehicle Click to see the video of an incident. What evidence is there that a huge force is acting on the vehicle during the collision? A loud noise can be heard The vehicle changes colour The vehicle changes shape and speed Jonathon and Stephen were playing a game of Gladiator Spinners as shown on the right. It is obvious to see the winner. Is there a force acting on both of the spinning tops? No Yes Complete the sentence below. Ï know that there is an unbalanced, contact a balanced, non-contact a net zero force acting on the spinning tops because I notice the direction of the tops constantly changing" Name a contact force acting on the spinning tops that will cause them to slow down. friction buoyancy gravity Click to see the movement of the two trampoline competitors. What forces are acting on these gymnasts? How do you know that there are forces acting on the two gymnasts? Which of the following words best describe the forces acting? Circle the appropriate responses. - balanced - unbalanced - contact - non-contact Explain your choice. A skydiver deploys her parachute, to descend back to earth slowly and with constant speed. What force/s is/are acting on the skydiver as she is falling back to earth just before her parachute is deployed? What force is increased by the parachute? Is there a net force acting on the skydiver as she descends with her parachute fully open? Explain. Click to view another skydiver . The image shows two forces acting in opposite directions and clearly shows their size in Newtons(N). What are the two forces shown on the diagram? Is there a net force acting on the skydiver? What will the size of the force acting in an upwards direction be when the parachute is deployed? less than 40N equal to 40N greater than 40N equal to 60N Consider the image of the paper boat floating on the surface of the water. Which of the following words can be used to explain these forces? 1) Unbalanced 2) Balanced 3) Zero net force 4) Net force 5) Contact 6) Non-contact Explain why you used the chosen words. View the video on the right. It shows sound speakers playing a sound. What evidence is there that a force is exerted by the speakers when it makes a sound? What evidence do you see that forces are acting on the tissue papers? This is caused by an electrostatic force of repulsion. Why do the tissue papers collapse when the machine is discharged? View the video on the right. Watch how air pressure crushes a tin can with ease. What observation informs us that a force has acted on the can? A student is seen to be rubbing a balloon on his blazer then bringing is close to a running tap. What observation make one think that a force is acting on the column of water? Is this force a contact or non-contact force. Explain Is this a force of attraction or repulsion? Explain.